Alarm sounded in room with a working gas-fire. Immediately turned off and the windows & doors opened. No-one suffered any CO exposure symptoms. However, I could not cancel the alarm with the reset button and had to remove the batteries. The installation has been checked & cleaned but no reasons for the event were found. Installed a different alarm along-side the KIDDE (1yr old M/N 900-0260 s/n 767499). Neither have alarmed over the following 24hrs. Can you make any suggestions very unsettling. Sincerely