Siren is designed for alarming people when fire hazard is detected to let them evacuate. LA-D is a loop acoustic siren which can work without any external power supply. It can work on addressable loop circuits / stub circuits of AWEX FAS system only. Maximum number of devices per loop depends on: wire type, other loop elements. LA-D siren have built-in detector base which lets use this device as sounder and detector at once.