First Alert ONELINK Combination Smoke And Carbon Monoxide Alarm SCO501CN3ST If you want to build an integrated smoke and carbon monoxide alarm system, but without the cost and hassle of retrofit wiring in your home, the First Alert ONELINK Combination Smoke Alarm and Carbon Monoxide Detector SCO501CN3ST is an ideal choice. This alarm provides ultimate protection from two deadly threats, and it is packed with innovative features that give you precious time in the event of an emergency. And because it is able to wirelessly communicate with other ONELINK alarms, this device can help you create a wholehome safety network.