Mains heat alarm cw 9v battery backup this ionisation smoke alarm runs on 230v ac mains power it has a 9v battery pack capable of lasting up to 4 years in standby mode it is capable of powering the alarm for up to 2 years without mains power the alarm gives a fire warning when adequate smoke enters the alarm there is an easy fit base that allows a very quick and simple installation of the smoke alarm other features include built in circuitry to aid suppression of voltage transients and rf