PI submission on the GPS Tracking of Migrants in the UK

Privacy International has made a submission to the Independent Chief Inspector of Borders and Immigration inspection of the Home Office Satellite Tracking Service Programme. We highlighted some of our concerns about the intrusive nature of location data as well as systemic failures relating to the quality of tags and battery life of devices which have a significant impact on individuals, as battery depletion can result in criminal prosecution.


Key findings
  • The UK Home Office has introduced the electronic monitoring of people on immigration bail using GPS tags. For certain groups this tagging is a mandatory condition of immigration bail.
  • Using GPS tags, the Home Office collects location data 24/7, minute-by-minute every day, thus substantially extending their powers of surveillance.
  • This 'trail data' is highly intrusive and reveals intimate details of an individual's life.
  • Those wearing tags are prohibited from contact sports such as football, hockey or rugby.
  • The Home Office will use trail data to consider prosecutions for breach of bail conditions; in decisions on further submissions and Article 8 claims; to share with law enforcement; and for data analytics purposes including behaviour mapping.
  • The system lacks adequate safeguards against unnecessary and disproportionate use.
  • The imposition of tagging cannot be challenged before the judge considering an immigration bail application, thus ousting judicial oversight at this stage, a fundamental safeguard against unnecessary and disproportionate use of tagging.
  • The data is collected and processed by Electronic Monitoring Services, a service run by company Capita.
  • There are systemic failures relating to the quality of tags in terms of battery life which can negatively impact an individual's immigration case.
  • There is no time limit for the requirement to wear a tag.
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Privacy International’s submissions for the Independent Chief Inspector of Borders and Immigration inspection of the Home Office Satellite Tracking Service Programme

The Home Office have introduced 24/7 electronic monitoring and collection of the location data of migrants via GPS ankle tags. This seismic change cannot be overstated. The use of GPS tags and intention to use location data, kept for six years after the tag is removed, in immigration decision-making goes far beyond the mere monitoring of bail breaches or to prevent absconding.

Location data (aka trail data) is highly intrusive information which provides deep insight into and reveals intimate details of an individual’s life. It can reveal everyday habits, permanent or temporary places of residence, daily or other movements, activities carried out, social relationships and social environments, medical concerns, religion, sexuality and family life, etc. 

There are systemic failures relating to the quality of tags and battery life of devices which have a significant impact on individuals, as battery depletion can result in criminal prosecution.

Read a summary on this page or download the full submissions below.


The seismic change resulting from the introduction of GPS devices by the Home Office for those on immigration bail cannot be overstated. This enables 24/7 monitoring of an individual’s location, as well as live tracking, meaning that you could follow an individual's movements in real time. The data is stored for six years after the tag is removed. All trail data is shared with the Home Office when there is a breach alert on the Electronic Monitoring System (EMS), allowing them to review this material for matters unconnected to the alert in question. This goes beyond the mere monitoring of bail breaches through Electronic Monitoring as provided for in statute.  

We are concerned there is a systemic failure relating to quality of the tags in terms of battery life which places a far more onerous requirement on individuals to charge for long periods of time with the tag attached to their leg. Battery life is an issue which has been noted in the recent reports of the HM Inspectorate of Probation and the Ministry of Justice in relation to GPS tags. Failure to charge is a breach of bail conditions, meaning upon breach notification all data can be shared with the Home Office and result in civil and criminal penalties.

Further a list of battery breaches leads to assumptions of non-compliance when the reality could be that the problem lies with the quality of the device. Thus, errors and inaccuracies in the recording of breaches of bail conditions, including battery issues, impact upon broader immigration enforcement and bail compliance reviews. This raises concerns about how complicated and difficult it may be for an individual to correct errors in breach notifications that are recorded on their immigration file.

The technical implications of the quality of the tags and whether their charging efficiency depreciates, has significant impact on the individual.

This intersects with concerns we have been alerted to which related to the poor administration of the EMS, confusing and contradictory statements regarding obligations and bail conditions. The HM Inspectorate of Prisons Report details several issues with the service provided by EMS.

The use of GPS tracking goes beyond the aim of monitoring bail breaches or preventing individuals from absconding. The Home Office plans to use trail data, being the location data collected by the tag and stored by the third-party commercial provider:

  • To consider prosecutions for breach of bail conditions.
  • In decisions on further submissions and Article 8 ECHR claims.
  • To share with law enforcement agencies.
  • For data analytics purpose including behaviour mapping and informing immigration policy.

The impact on individuals who are subject to this surveillance is little understood or examined. There has been no equality impact assessment. Unlike the use by probation in the criminal justice system where GPS tags are used to work with an individual who is on probation, in the immigration context it is a punitive method of surveillance. We understand that the exemptions to mandatory electronic monitoring are being applied in a highly restrictive manner by the Home Office and the inability to challenge the Home Office imposition of tagging before a judge of the First-tier Tribunal has ousted a fundamental safeguard against unnecessary and disproportionate use.

This type of constant surveillance has been reported by the Ministry of Justice to negatively impact tag wearers leading to feelings of increased anxiety. In addition, individuals might not want to spend time with a friend who is wearing a GPS tag. It therefore risks having a strong chilling effect on the exercise of fundamental rights and freedoms. This is in the context of an absence of time limit for tags or safeguards for those wearing tags to ensure they are applied in a manner which is necessary and proportionate.

In addition to their intrusive nature, the device limits the way an individual can live their life, not just with the burden of regularly charging the device, but the tag prohibits contact sports such as football, hockey or rugby.

The Technology

The Home Office previously used Radio Frequency tags for electronic monitoring. They have rolled out the use of GPS tags and have proposed the use of smart watches. The Home Office states that the GPS devices they use have dual capability to use GPS and radio frequency technology. 

The full submission which can be downloaded below, details the contracts procured by the Ministry of Justice for electronic monitoring.

Radio Frequency

Traditional radio-frequency tags rely on two different elements, a base station usually located in the individual’s house and connected to the network and a tag attached to the individual. They are typically used to enforce curfew conditions, such as that an individual remain at home from 7pm to 7am. The tag communicates with the base station (monitoring unit) over a specific radio frequency to detect if it is within range.

The locational information is essentially binary though: in other words, in terms of “location” it can only indicate whether the tag is present or is not present within the range of the home monitoring unit. The tag only “communicates” with the monitoring unit and it is the monitoring unit that sends the information back to the monitoring company. So, the two pieces of equipment need to be within range of each other for locational information (such as whether the tag is present) or other information (such as whether the tag has been tampered with) to be registered by the monitoring unit.

If the tag fails to report (or the signal is below a threshold) then it will raise an alert, and a specified number of alerts over a timeframe will prompt the tagging authority’s control centre to phone the tag wearer on their landline. If this fails, the control centre may ask law enforcement to visit the address and ascertain if the wearer has absconded.


Whereas radio-frequency tags tell the tagging authority whether the tag wearer is observing a curfew, i.e., that the tag is within the vicinity of the monitoring box, GPS tags provide the authority with a complete location history, that is a log of where the tag was minute-by-minute of every day. This information can be accessed directly by control-centre personnel and can be monitored by software.

GPS tags enable geolocation by receiving signals from at least 4 different satellites and doing some maths to pinpoint location. A GPS navigation chip will calculate and store location data and a SIM card connects the tag to the mobile network.  The mobile phone network is what is used to communicate the location information to a central computer at a monitoring centre in “real time”. The central control then may use a mapping service to plot locations and times.

Anyone who has used a GPS-based smartphone app such as Google Maps will have seen something very similar to how GPS tags work; the app will record your location on the Earth’s surface.

Tags can collect GPS location data at different frequency of intervals. For example, the buddi ST3 Smart Tag 4 indicates the ability to set intervals at either 15 minutes, 30 minutes or an hour. Its specification states: “GPS Location (Intervals can be defined or a real-time request made)”. If you collect it at a lower frequency, you collect less location data. The ‘Attenti One Piece Tracking Device’ states in its manual that in Active Mode, “The standard 1 Piece call-in interval is once every hour while in compliance”, while in Passive Mode, “the standard 1 Piece call-in interval is once every six hours.”

According to one company which sells GPS tracking devices to industry, some devices do not use intervals at all and instead use on-demand tracking. This means that they only turn on in response to a specific location request.

It is possible for GPS tags to create inclusion and exclusion zones. As noted by Buddi who have a pilot project with The Mayor’s Office for Police and Crime, London, [‘MOPAC’], their tag features inclusion zones which are areas on a map to indicate where the device should be located during set times of the day and exclusion zones which are set up customisable zones to trigger alerts when the device enters the specified zone.

The GPS tag itself is usually attached to the ankle, using a reinforced band. The physical tag consists of the tag attached to the individual. It has been described in the Scottish Government consultation report as larger and heavier than radio-frequency tags. This is the result of it having to accommodate a larger battery. The physical implications of this are that contact sports such as football, hockey or rugby are not allowed according to guidance documents.

Smart Watches

The Home Office have not commenced use of smartwatches, but indicated an intention to use them. The smartwatch will most likely rely on GPS technology to track the location of the wearer, similar to how the GPS tags operate.  However, the smartwatches introduce the additional element of biometrics.

The Home Office’s 2021 DPIA states that:

“The new Smartwatch device that we will be using for monitoring purposes via inclusion exclusion zones and collection of Biometric Facial Image checks is new technology and is currently still undergoing checks. It will be supported by MOJ and HO DDAT. The Smartwatch devices will not be available until November 2021 and any emerging risk will be included and assessed within this DPIA.”

Biometric Facial Image checks will be used to ensure that the individual subject to bail monitoring is the individual who is wearing the watch, i.e., to check that they have not taken it off or someone else is wearing it. This is the alternative to having a tag fitted to the ankle with a tamper resistant tag that cannot be removed.

On 3 May 2021 the Ministry of Justice awarded a contract to Ingenium Biometric Laboratories Limited for ‘Assurance testing for the use of biometric-enabled wearable/non-fitted devices as an alternative to electronic tags.’  The requirement is for ‘biometrics assurances services; test and evaluation of biometric products; biometric assurance plan and strategy’. The contract highlights some of the risks associated with biometrics devices, being false matches and bias in age, gender or ethnicity.

Biometric images being held on the supplier’s database raise concerns, particularly in the present context where there are, inadequate safeguards against the misuse and abuse of GPS location data, and where there is little detail on the system that the Home Office intends to use or is procuring in order to implement the use of smart watches. There is risk associated with opaque systems including how they actually work and why and how they can fail.

Biometrics is the “measurement of unique and distinctive physical, biological and behavioural characteristics used to confirm the identity of individuals.” There are two parts to the use of any biometric system. Firstly, biometric technologies capture and store characteristics in a database to identify an individual. Secondly, the information in this database is cross-referenced to verify or authenticate an individual’s identity – image verification via monitoring checks.

The Home Office’s proposed use involves a 1-1 match of the individual against the stored template to answer the question, “is this x?”. Biometrics can also be used to identify an individual – this is a 1-to-many match, to answer the question “Who is this?”.

The use of biometrics presents a unique set of concerns. In 2018, the United Nations High Commissioner for Human Rights issued a Report on the right to privacy in the digital age, which highlights significant human rights concerns with the creation of mass databases of biometric data:

“Such data is particularly sensitive, as it is by definition inseparably linked to a particular person and that person’s life, and has the potential to be gravely abused.

For example, identity theft on the basis of biometrics is extremely difficult to remedy and may seriously affect an individual’s rights. Moreover, biometric data may be used for different purposes from those for which it was collected, including the unlawful tracking and monitoring of individuals. Given those risks, particular attention should be paid to questions of necessity and proportionality in the collection of biometric data. Against that background, it is worrisome that some States are embarking on vast biometric data-base projects without having adequate legal and procedural safeguards in place.”

When adopted in the absence of strong legal frameworks and strict safeguards, biometric technologies pose grave threats to privacy and personal security, as their application can be broadened to facilitate discrimination, profiling and mass surveillance.

The varying accuracy and failure rates of the technology can lead to misidentification. As the UK’s National Cyber Security Centre puts it “...no two captures of biometric data will produce truly ‘identical’ results. So, a biometric system must make an estimation as to whether two biometric samples come from the same individual.”

Trail Data

Trail data refers to the complete location history of the person who is wearing the tag (or a smart watch), i.e. a log of where the person has been minute-by-minute every day.

GPS monitoring provides deep insight into and reveals intimate details of an individual’s life. It is highly intrusive, reveals sensitive information, and the longer the tag is in place, the greater the volume of location data collected and thus the ability to have insight into an individual’s patterns of behaviour.

The data collected may also include the time and length of time that devices are charged, revealing patterns of behaviour.

Although GPS technology allows for technical measures to limit the amount of data collected to what is necessary to make the tagging effective, this does not appear to be a feature of the tags procured by the Ministry of Justice, either in the immigration or criminal justice context. The tags used by both the criminal justice and immigration context do not appear to have the ability to limit the amount of data collected so that the data gathered and retained is only what is necessary to monitor bail compliance and/or minimise the risk of offending.

The intrusive nature of trail monitoring and lack of safeguards

The use of GPS tags is a significant change in the surveillance of migrants. The Home Office have not adopted a method of collecting location data by intervals, but instead is doing this 24/7. GPS tags thus enable constant monitoring of an indivduals’ location and the colletion and storage of this data for passive review and analysis.

GPS location data provides deep insight into and reveals intimate details of an individual’s life. It reveals everyday habits, permanent or temporary places of residence, daily or other movements, the activities carried out, the social relationships of those persons and the social environments frequented by them. It also reveals sensitive information such as potential medical concerns if they visit a particular medical clinic, religion if they visit a place of worship, political beliefs if they attend a protest, rally or political party headquarters, sexual orientation if they visit certain places or advice centres, and other intimate details of their privacy and family life (if they attend schools or nurseries, playgrounds, other residences, etc).

In the US Supreme Court Judgment of United States v Jones, law enforcement installed a GPS tracking device to the undercarriage of the Jeep of a suspect and tracked the vehicle’s movements over the next 28 days. Justice Scalia, delivering the opinion of the Court noted the volume of data that this period generated stating:

“By means of signals from multiple satellites, the device established the vehicle’s location within 50 to 100 feet and communicated that location by cellular phone to a Government computer. It relayed more than 2,000 pages of data over the 4-week period.”

The volume and granularity of data is likely to considerably increase when the tag is attached to a person, instead of a vehicle which is only used a few times a day on certain days.

The US Supreme Court discussed the intrusive nature of GPS monitoring and how it chills associational and expressive freedoms. For individuals themselves, it’s unclear whether they understand the volume of information generated as a result of 24/7 monitoring and that the data can be aggregated, such that the government will be able to ascertain, more or less, their political and religious beliefs, sexual habits, etc.

“GPS monitoring generates a precise, comprehensive record of a person’s public movements that reflects a wealth of detail about her familial, political, professional, religious and sexual associations…(“Disclosed in [GPS] data … will be trips the indisputably private nature of which takes little imagination to conjure: trips to the psychiatrist, the plastic surgeon, the abortion clinic, the AIDS treatment center, the strip club, the criminal defense attorney, the by-the-hour motel, the union meeting, the mosque, synagogue or church, the gay bar and on and on”). The Government can store such records and efficiently mine them for information years into the future. … And because GPS monitoring is cheap in comparison to conventional surveillance techniques and, by design, proceeds surreptitiously, it evades the ordinary checks that constrain abusive law enforcement practices…”

“I would also consider the appropriateness of entrusting to the Executive, in the absence of any oversight from a coordinate branch, a tool so amenable to misuse …”

In the Council of Europe, Recommendation CM/Rec(2014) 4 of the Committee of Ministers to member states on electronic monitoring noted that:

“…electronic monitoring technologies should be used in a well-regulated and proportionate manner in order to reduce their potential negative effects on the private and family life of a person under electronic monitoring and of concerned third parties” and that there should be “rules about limits, types and modalities of provision of monitoring technologies … in order to guide the governments of the members Sates in their legislation policies and practice in this area”.

“…that ethical and professional standards need to be developed regarding the effective use of electronic monitoring in order to guide the national authorities, including judges, prosecutors, prison administrators, probation agencies, police and agencies providing equipment or supervising suspects and offenders”.

On 26 November 2018, Privacy International submitted its legal briefing to the Court of Justice of the European Union (CJEU) on the case of LQDN, FDN and others v. France, concerning the retention of personal data under French law. On 6 October 2020 the CJEU issued its judgment on joint cases against France and Belgium. In this decision of the Grand Chamber of the CJEU in Joined Cases C‑511/18, C‑512/18 and C‑520/18, the intrusive nature of location data was considered:

“117. That conclusion is all the more justified since traffic and location data may reveal information on a significant number of aspects of the private life of the persons concerned, including sensitive information such as sexual orientation, political opinions, religious, philosophical, societal or other beliefs and state of health, given that such data moreover enjoys special protection under EU law. Taken as a whole, that data may allow very precise conclusions to be drawn concerning the private lives of the persons whose data has been retained, such as the habits of everyday life, permanent or temporary places of residence, daily or other movements, the activities carried out, the social relationships of those persons and the social environments frequented by them. In particular, that data provides the means of establishing a profile of the individuals concerned, information that is no less sensitive, having regard to the right to privacy, than the actual content of communications (see, to that effect, judgments of 8 April 2014, Digital Rights, C‑293/12 and C‑594/12, EU:C:2014:238, paragraph 27, and of 21 December 2016, Tele2, C‑203/15 and C‑698/15, EU:C:2016:970, paragraph 99). […]

The limitations of electronic monitoring: accuracy and battery life


Global Positioning System (GPS) is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the earth. GPS monitoring uses a network of 30 US maintained NAVSTAR satellites to calculate the physical position of the GPS tag. Although other networks of satellites do exist (Glonass, Galileo, Compass) they are not yet ready for use.

The Scottish Government consultation in 2013 highlighted a number of problems with GPS tags:

  • “GPS usually works in most domestic homes, but may not work inside all buildings;
  • GPS usually works whilst travelling in cars, however, may not work on trains;
  • GPS drift (movement in accuracy of signal) might occur when static for long periods of time and near waters;
  • GPS accuracy is affected by nearby tall buildings and does not work underground.”

“There are no absolutes about accuracy or performance of any GPS device. However, we can reliably say what the likely accuracy of any one “fix” is within a particular range. (A fix is where the GPS system locates the tag in a particular place at a particular time). Depending on the strength of signals to the nearest satellites a fix might be accurate to 2-5 meters, 5-10 meters, 10-20 meters etc. “No absolutes about accuracy” does not mean the data can’t be used it just means that whoever is using it needs to understand the difference between fixes that are accurate to 2 meters as compared to entries that are accurate to 20 meters. Additional assurance can be gathered from multiple fixes. So, if an offender has generated 20 fixes or data points at regular intervals on a map within 5 minutes, whilst any one point may be subject to drift, nineteen others showing an offender proceeding in a certain direction gives you a great deal more certainty about the result showing his or her movements.”

Battery Life

EMS state in their YouTube video hosted on the HM Prison and Probation Service channel that GPS tagging devices need to be charged for an hour a day.  This is also stated in the “tagging handbook” published on the government’s website. A handbook on GPS tagging from the Ministry of Justice, however, suggests that fully charging a tag usually takes “at least 2 hours every day”.

Battery life in GPS tags is a recognised problem. This has been noted in the recent reports of the HM Inspectorate of Probation and the Ministry of Justice. The Ministry of Justice evaluation of GPS tags in 2019 noted that:

“Forty-three per cent of violations were due to tracker shutdowns resulting from loss of the tag’s battery power due to insufficient charging – potentially representing the ‘burden’ of wearers having to charge the battery daily”

The design of the tagging system contributes to the drain on the battery due to the use of live location tracking. The Reform report ‘Cutting crime: the role of tagging in offender management’ dated September 2015 states that:

“1.6.1 As pressure rises to ensure GPS devices run more and more concurrent capabilities, the battery life reduces significantly. In addition, increasing volumes of data transfer drains the battery life of a device. Continuously tracking offenders to provide real-time intelligence requires much more frequent communications between the electronic anklet and central portal. Interview for this report suggest that this type of tracking can reduce a tag’s battery life to just a few hours…”

The ICO has commented that:

“While advances to battery technology have increased in recent years, GPS can be very draining on batteries and battery life depends on the frequency with which the system provides updates on locations (every 10 seconds, every 30 seconds, every minute etc).”

Failure to charge is a breach of bail conditions, meaning that if the battery is depleted, all data (including trail data) can be shared with the Home Office, and this can result in civil and criminal penalties relating to the breach, but it can also be used for unrelated matters.

When the battery runs low, the tag will vibrate and the power light will flash red on the tag until it is charged. This can of course happen at any time of the day or night, thereby waking people up in the middle of the night. It may also occur in public spaces, thereby exposing the fact that the individual is wearing a tag.

If the battery begins to fail, it will be necessary to charge devices for much longer periods of time and more regularly with, of course, the tag attached to the individual’s leg, thereby limiting their freedom of movement considerably beyond what is intended through the imposition of the electronic monitoring condition. This is a particular concern if the battery degrades to the point that multiple charges need to occur within a single day.

The individual can be given a portable charger which they can bring with them to charge a device if they are out and about. However if the device is faulty and will not charge properly when connected to the mains, then a portable charger will face the same problems with being unable to effectively charge the device and making the device hold a charge.  Thus, a portable charger is not an answer to a faulty device. 

Concerns about purposes of trail data processing

The Home Office has set out several uses for trail data.

“trail data will be held by the EM supplier but may be accessed by the Home Office where one or more of the following applies and where proportionate and justified in the circumstances in accordance with data protection law:

  • a breach of immigration bail conditions has occurred, or intelligence suggests a breach has occurred to consider what action should be taken in response to a breach up to and including prosecution
  • where a breach of immigration bail conditions has occurred, which has resulted in the severing of contact via EM, trail data will be used to try to locate the person
  • where it may be relevant to a claim by the individual under Article 8 ECHR
  • to be shared with law enforcement agencies where they make a legitimate and specific request for access to that data
  • Anonymised data may be used to understand the impact of EM and the behaviours of those on EM to continuously improve the service and to inform immigration policy in accordance with data protection law.”

In relation to the ability to access trail data where relevant to ‘a claim by the individual under Article 8 ECHR’ the DPIA states that the trail data will negate the need to request evidence from third parties:

“In the event of the receipt of Article 8 representations or further submissions from the individual, authorised Home Office staff dealing with those submissions may request access to the full trail data to support or rebut the claims. This will hopefully negate the need to request ‘substantiating’ evidence from third party’s which can cause unnecessary delays in considering the claims.”

This puts an enormous burden on an individual to recall events recorded by the GPS tag, which could be years in the past. It shows no appreciation for issues relating to accuracy. It is also deeply concerning that the Home Office would seek to make life changing decisions on an individual’s future purely based on location data and without evidence from third parties. Previously the only thing an individual would need to remain conscious of during their bail is to comply with their conditions, now they will need to think about how every single one of their movements might impact their Article 8 representations or further submissions.

There do not appear to be any safeguards in place to address the imbalance this creates between the tagged individual and the SSHD. For example, there are no arrangements for prior independent authorisation for access to such intrusive data.

As BID have stated:

“Article 8 claims can be very broad and involve a lot of personal and private details about an individual’s life. Presently there is no clear limit on the circumstances in which location data might be deemed by the Home Office to be relevant to an Article 8 claim. This could mean that whenever an individual makes an Article 8 claim the Home Office would have the right to access all their ‘trail data’ on the grounds that it ‘may be relevant’.

This provision gives unlimited discretion to the Home Office decision-makers to retrospectively access location data for purposes over and above monitoring compliance with bail conditions. The Home Office is not a neutral third party and they have a vested interest in proceedings which could have negative repercussions on an individual’s substantive case. This can be contrasted with the use of electronic monitoring in the criminal justice system, where electronic monitoring data must only be processed for specified, explicit and legitimate purposes”.”

Table of Contents
  • Introduction
  • The technology and how it works (radio frequency, GPS tags, smart watches)
  • The intrusiveness of location data
  • Quality and accuracy issues: accuracy of location data and battery life

Personal Data

Information that can help identify an individual or can even make an indvidual identifiable.