Hi - I have 4 older e150 main powered smoke detectors in my house. The one installed underneath the staircase between the 1st and 2nd floor started chirping (every minute) for a few hours yesterday before going silent. it started this morning again so i dismounted (no electrical connections anymore) the smoke detector (lets call it A) and after one hour the chirping stopped but resumed again for the whole afternoon until 10pm.  i dismounted another smoke detector (lets call it B) on the basement ceiling but the chirping continued (coming from where A was)

i decided to cut the power off to all 4 smoke detectors but the chirping continued, preceded by one very loud beep shortly before the chirp (every minute also) coming from where A was. so it looks like there is something making chirping and beeping noises even with no power at all in the house and two smoke detectors completely disconnected. I have to my knowledge no CO detector, nothing else in the vicinity. how come that when i cut the electricity i get a very loud, regular beeping sound looking like it is coming from A wires (i have dismounted A). the chirping noise is hard to localise but the beeping is so loud there can be no mistake. there should be nothing left that makes a loud beep (the same intensity as if there was a fire alarm) except there is no power in the house and no smoke detector anymore there. 

i cannot understand what happens can anyone please help? as i fish typing this the chirping has stopped but i am pretty sure it will start again and it is driving me nuts. thanks for your help  

 

 

Have you taken the battery out of each smoke detector? (You only mention removing the mains)