Electronic monitoring (EM) was implemented in the United Kingdom under the Criminal Justice and Public Order Act 1994. EM is a surveillance tool designed to track offenders and suspects, verify their whereabouts and determine whether they are complying with a set of ‘liberty’ conditions imposed by a court or government authority under the Asylum and Immigration (Treatment of Claimants) Act 2004, the use of this technology was extended to immigration controls. Individuals subject to immigration control and deemed as ‘high risk’ of harm, reoffending or absconding could from then on be fitted with an ankle device and subjected to curfew conditions. The initial devices were equipped with radio-frequency technology, designed to measure the distance between a tag and its base unit, to establish whether they were at home or not. However in 2021, the Home Office adopted a new generation of ankle tags, equipped with a fundamentally different and more intrusive technology—Global Positioning System (GPS ankle tags). These tags monitor an individual’s precise geolocation continuously, gathering a vast amount of data. Records of subjects’ geolocation data are then stored and retained for years, available for authorities to access for a wide variety of purposes. In 2022, the EM provision was extended to asylum seekers who recently arrived on boats and via other irregular means. In this chapter, we shed light on the evolution of tagging technology, the privacy intrusions involved and resulting breaches of data protection law, and how it is experienced by racialised minorities. We conclude by outlining the ongoing resistance against EM harms by third sector organisations and legal professionals. The chapter uncovers the racial dynamics of the technology, and adds to the literature on migration, surveillance studies, critical data studies and state racism.