Alarm systems

An alarm device comprises an RF receiver, an RF transmitter, and a controller which acts as a repeater. The controller directs repeating of received messages according to repetition level in a repeated message, it reads repetition levels in received messages, and it decides on repeating received messages according to the repetition levels. It does not repeat a message which has already been repeated a maximum threshold number of times, in one embodiment three times. The controller is adapted to time out and re-sets cycles of monitoring repetition levels, and to cancel messages which are held without being repeated for a maximum period of time. Also, the controller performs house coding by in a first phase transmitting and re-transmitting its coding message, and in a second phase repeating house codes it has learned.