The First Alert BRK PRC700 Battery-Operated Smoke and Carbon Monoxide Alarm features a photoelectric smoke sensor and an electrochemical carbon monoxide sensor. The photoelectric sensor detects larger smoke particles from smoldering fires from objects like cigarettes burning on furniture or in trash cans. The alarm features a loud, 85-decibel alarm, designed to wake even the soundest of sleepers. One button silences any nuisance alarms, and also tests detector functions, while lights indicate if the alarm detects smoke or carbon monoxide. The battery-operated smoke and CO detector can be installed easily, with no wires or electrician required, and its slim profile will seamlessly blend in with your home decor. The detector will continue monitoring during power outages, and its twist-lock mounting system makes replacing batteries easy.