The First Alert SCO501CN3ST Wireless Interconnected Smoke and Carbon Monoxide Alarm with Voice and Location detects both smoke and carbon monoxide. It is a wireless-enabled, battery-operated detector that features an 85dB alarm plus a voice alarm to let you know where the danger is. This technology allows other compatible First Alert wireless-enabled alarms located in several areas of your home to communicate with each other, alerting you to a problem early even when it's on another floor. The smoke and carbon monoxide detector features a photoelectric smoke sensor and electrochemical carbon monoxide sensor.