? BSEN 50291 approved ? Battery life over one year ? Low battery warning signal ? End of sensor life warning ? Memory function ? Delay warning signal to avoid nuisance ? Green LED flashes once every minute indicate normal operation ? Yellow LED flashes indicate low battery & /or sensor fault ? Red LED flashes indicate alarm function ? Test push button to test function & circuitry ? Silencer (hush) feature ? Automatic self test 1 x per minute ? 85dB at 3 m loud tone ? Easy & simple to install ? 6 years CO alarm with built-in sealed battery available