I have an Ei 144 heat alarm in the kitchen, an Ei 141 in the hall and another on the landing. The one on the landing started beeping every 40 secs. I have disabled all alarms at the fuse box and no green lights are visible, I have taken all 3 units off the base units and taken out the batteries and still every 40 secs the base unit on the landing keeps beeping. Will it run out of energy and how long will this take? Thanks.

Hi Mark, assuming this is the standard base plate of the Ei series, there is no sounder in the base plate. So the sound is likely to come from a CO alarm with a dying battery in the vicinity. 

Maybe in a drawr or similar. It is very difficult to spot the source of an occasional beep.

Harry