55000-852APO Sounder Circuit Controller with Short Circuit Isolator55000 852APO Sounder Circuit Controller with Short Circuit Isolator Manufactured by Apollo, this Apollo Sounder Circuit Controller Short Circuit Isolator is used to control the operation of a zone of conventional sounders and report their status to the control panel. Compatible with any fire panel using XP95 or Discovery protocol the 55000 852APO Sounder Control Unit is used to control the operation of a zone of conventional sounders and report their