Abstract: A security system including a hand-portable wireless communicator having two keys for selecting and executing signal transmissions that control the system. The function of each key is determined by the order in which the keys are actuated, so the first actuated key selects the mode of operation and the other key executes the transmission. Sequential actuation of the keys, first one and then the other, initiates a test. Simultaneous actuation of the keys initiates an alarm. Multiple actuation of the same key cycles through alternative modes of operation, like armed, partially armed or disarmed. Transmission of a signal representing the selected mode is then initiated by actuation of the other key. A reset mechanism reinitiates the key functions after a predetermined time interval, so the key function is determined based on an order of actuation after said reinitiation.