Effectively protect your family from carbon monoxide hazards with the First Alert(R) plug-in alarm with AA backup battery. It has an electrochemical sensor reacting to carbon monoxide particles by creating an electric current that sounds a loud 85 dB alarm signal. A single Test/Silence button lets you test the alarm or to turn off the audible signal in the event of a false alarm. Finally, it has a low battery indicator as well as an end-of-life signal. Backed by a 7-year limited warranty.