I have 4 smoke/fire and carbon monoxide detectors that are hard wired and have 9 volt battery back up system. They all went off in the middle of the night for no reason. The fire department came to my house, and told me to simply replace them. I went out and bought 4 new ones, installed them, and as soon as I turned on the circuit breaker the alarms started going off again. It's not dust, and the batteries don't need replacement, all 4 are brand new. What could be causing this problem?