This First Alert SA511CN2-3ST Interconnected Wireless Smoke Alarm with Voice Location features an 85-decibel siren and voice alarm with 11 programmable locations that tells you where the danger is located. A photoelectric sensor detects smoke while minimizing false alarms from cooking or shower steam. These interconnected smoke detectors come in a convenient pack of 2 and are designed to work together throughout your home, with one alarm triggering the other alarm during an emergency, creating a home safety network. You can wirelessly connect it with up to 18 other First Alert enabled alarms in your home. The battery-operated alarms don't require hardwiring for installation and will provide con tinued monitoring even in the event of a power failure.