The Ancillary Base Sounder is a local-area sounder designed for indoor use. It can be connected only to detection systems using Discovery or XP95 detectors and control panels with appropriate software. The Ancillary Base Sounder is loop-powered and requires no external power supply. It operates at 17–28V DC.
 
The sounder incorporates a base into which a loop-powered beacon or an XP95 or Discovery detector is fitted. It is powered by the control panel via the loop wiring to which it is connected. Since the sounder is switched by the remote indicator output of the associated detector or beacon no remote indicator facility is available. A guaranteed sound output of 85dB(A) at 1 metre is achieved at a current consumption of only 3mA. The sounder generates very low current noise so that up to 126 sounders may be connected to a loop. The Ancillary Base Sounder responds to signals from the associated detector or beacon. It does not have an address of its own.