Purchased 4 Kidde P12040 in 2011. Last night those 4 alarms went off. I shut off the AC BK but they continued to sound. Pulled the 9V batteries out, a very bad thing! Grandchildren most sleep! This Am reinstalled 9V's & activated the AC. Alarms sound pattern was 3 short and a pause then 1 beep.It was repeated many times until AC off. Looked a Kidde guide for a sounding code, NONE! Please inform me why this is happening! Should I replace the alarms? Martin Walicki