It might be connected to the smoke detectors and there might be a wireless flood detector somewhere or they maybe using it for inactivity detection, a lot of councils have made it a rule that if the sheltered tennant is not getting daily calls to check they are ok then there must be automatic inactivity detection. Its unlikely the landlord fitted it for no reason there must be some requirement for it, either insurance or council rules, removing it is not a good idea if you are going to fit another fit it alongside.
Contact the landlord before messing with it to make sure.