FIRST ALERT SA520CNA-3ST OneLink™ Photoelectric Smoke Alarm Wireless 120 VAC/VDC

120 VAC/AA battery back-up/wireless interconnect. Easily expand an existing interconnected 120 V AC system by replacing one alarm in the series with this alarm. Add additional battery-operated First Alert ONELINK enabled alarms to expand without wires. Optipath 360 technology - patented photoelectric smoke sensing design. Spread spectrum horn - easier for elderly with normal hearing loss to hear. Two Latching features - alarm latch and low battery latch. Two silence features - silence low battery chirp for up to 8 hours or temporary silence nuisance alarm conditions. 10-year warranty.