Most of these also have dual battery/120v power. So there are usually 3 wires coming into the alarm: two (black + white) for 120v power and the third (red) for

Most of these also have dual battery/120v power. So there are usually 3 wires coming into the alarm: two (black + white) for 120v power and the third (red) for 9v signal. The usual way around this feature/problem is to disable (disconnect) the signal line at each alarm.