Abstract: A transmit-receive burglar alarm system provides for code changing so that the user may readily change the transmitted code to which the system will respond. The transmitter is battery powered, and the transmission circuits are disabled except during transmission intervals to conserve battery life, the transmitter transmitting a weak battery signal when the battery voltage falls below a prescribed level, the receiver providing a distinctive signal in response thereto. The transmitter may select one of two channels at the receiver depending upon the desired response and may also select a delayed or immediate response if the receiver is in the delay mode. The home or base station includes a receiver and a microprocessor to determine first if the transmitted code is proper to respond to and then on which of two channels the response is to be indicated; the channels determining the format of the audio signal to be generated both on internal and external audio devices.