When we moved from one house to the next I needed to replace smoke detectors in order to get a CO. I do so, but developed a chirp. Since the system is all hooked together (or so it seemed) I couldn't figure where the chirp we emanating from. I tried for hours. I mean, seriously, hours. At some point I went to toss something away in the kitchen trash can and 'chirp.' It was one of the detectors I had replaced and thrown away.