Hoyles GX20e Gemini Battery Powered Fire Alarm is the simplest and most economical form of electrical fire alarm available. It features an integral call point and a high-power (105db @ 1m) piezo electronic sounder. A key switch is used to silence or restart the alarm. Powered by two PP3 Alkaline batteries that have a life expectancy of about 12 months depending upon usage. A battery condition monitor is incorporated to warn of impending battery failure. The GX20e is intended as a manual fire alarm for small buildings where a single standalone system is sufficient, however, up to four units can be linked together. It is not possible to install additional individual call points or sounders.