First Alert, Wireless Interconnected Photoelectric Smoke & Carbon Monoxide Combo Alarm, With Voice & Location, Detects Smoke & Carbon Monoxide, Can Work With Compatible Models To Create A Wireless Alert System, Additional Alarms Not Included, Designed For Wireless Connectivity With No Hardwiring, Battery Operated Detector Can Communicate With Up To 16 First Alert Wireless Interconnected Alarms, So You Can Be Alerted To A Problem Early, Even When It's On Another Floor, An 85 Decibel Siren As Well As A Voice Alarm Will Sound To Let You Know Where The Danger Is, & Whether It Is A Smoke Or Carbon Monoxide Emergency, Features A Photoelectric Smoke Sensor & Electrochemical Carbon Monoxide Sensor For Advanced Detection.