It's a Z-Wave device that listens for your existing smoke detectors to go off then will send a z-wave notification. One sensor is supposed to work for an entire house.
This Z-Wave Smoke Detector Listener sends signals to Z-Wave networks based on existing smoke and CO detectors. Improve your home's safety system with the Ecolink FireFighter Wireless Audio Detector. SKU: FF-ZWAVE5-ECO