Potentially dangerous psychiatric patients are being fitted with GPS tracking devices to prevent them absconding on day leave.
The South London and Maudsley NHS Trust has attached the £600 ankle devices on more than 60 medium and high risk patients under the pilot scheme.
The trust said it had consulted patients and families.
The devices, which can track a person's location to within a few yards, are already used for dementia sufferers.
They came into use in south London after rapist Terence O'Keefe, 39, escaped from custody at King's College Hospital before strangling 73-year-old David Kemp.
A spokesman for the trust said: "We have a duty to provide high-quality patient care while at the same time promoting public safety.
"Our medium secure services provide hospital treatment for people with severe mental health problems - many of whom have restrictions placed upon them by the courts.
"We are currently exploring the use of a tracking system to help us provide safe, secure and effective services."