The U.K. is presenting asylum seekers with an ultimatum: await deportation and asylum processing in Rwanda, face detention or wear a tracking device. Or leave voluntarily.

As thousands of people continue to arrive in the U.K., the British authorities are scrambling for new ways to monitor and control them. Under the government’s new rules, Britain has a legal duty to detain and deport anyone who arrives on its shores via truck or boat regardless of whether they wish to seek asylum. Passed in July 2023, the Illegal Migration Act has already been described by the United Nations Human Rights Office as “exposing refugees to grave risks in breach of international law.”

More than 20,000 people have come to the U.K. on small boats so far in 2023, and some 175,000 people are already waiting for an asylum decision. But officials say the U.K. does not have the physical space to detain people under the new law. And a public inquiry published this week argued that the U.K. should not detain migrants for more than 28 days. The report found evidence of abusive, degrading and racist treatment of migrants held in a detention center near London’s Gatwick Airport.

With detention centers at capacity and under scrutiny for mistreating migrants, and with the Rwanda scheme facing court challenges, those awaiting deportation or asylum proceedings are increasingly being monitored using technology instead, such as GPS-enabled ankle trackers that allow officials to follow the wearer’s every move. The ankle tracker program, which launched as a pilot in June 2022, was initially scheduled to last 12 months. But this summer, without fanfare, the government quietly uploaded a document to its website with the news that it was continuing the pilot to the end of 2023.