The 755PSMA4 smoke alarm is a photoelectric smoke alarm that can be used as a single mains powered, battery backed alarm or can be interconnected with other 755 series smoke alarms to give whole home protection. It is designed to be surface mounted on the ceiling. When used with the 755RFB (wireless mounting base), the alarm can offer wireless or wired interlinking capabilities as well are remote test/hush wired functionality. When used with the 755RB (relay mounting base), the alarm can be used to connect to 3rd party devices such as lights, sirens and home automation systems through a voltag...