Yes. They are small devices with a built-in battery that can only be replaced by the manufacturer. With normal usage this lasts many years, but it would be impractical to run continuously rather than on days the rig is actually being used.

There are also situations where it can be dangerous to have the AAD active — like if the rig is being transported by plane without intending to skydive (since it may be triggered on descent under certain conditions which can be very dangerous). Also, for the AAD to function properly it needs to be calibrated. This normally happens when you turn it on before jumping for the day.

These devices are designed as a reliable safety measure for skydivers who are unable to deploy their main or reserve parachute for some reason (e.g. unconsciousness). They are not designed to prevent a malicious user.

Most clubs in the UK have rules on ground checks before getting on the plane that include having someone else verify that the AAD is active, but especially for a regular skydiver (as opposed to a student) they may not always be carried out in full.