The RAD-16LS is a sixteen zone interior radio box that complies with NFPA 1221. Each zone is end-of-line resistor type with 4.7K Ohms as the standard value. Ground detection is built-in for both sides of each zone connection. The unit consists of 12VDC battery, AC transformer, microprocessor control board, and AM or FM radio transmitter. Built in features include battery charger, watchdog timer, auto restart, clock circuit, alarm/trouble visual and audible indicators, zone bypass, local FORM C trouble relay, AC power fail and low battery detection, fuse blow circuit, and a processor stop circuit should battery voltage drop below 8.5 VDC. The RAD-16LS is completely compatible with existing 1221 Radio formats. A 24-hour test clock operates on 60 Hz with crystal backup in case of power failure.