ZETA ZT-MS Mains Photoelectric Smoke Alarm with 9V Battery provides smoke detection and alarm functions within a single unit. Advanced electronics in conjunction with a photoelectric smoke sensing chamber provide early detection of smoke and high immunity against unwanted alarms. ZT-MS AC/DC smoke alarms are mains powered, with battery backup, suitable for general residential applications. ZT-MS AC/DC smoke alarms provide homeowners and installers with an easy-to-install, premium solution for life safety and efficiency and accuracy.