I guess the detector is working. I've had no false alarms or readings on the screen. As others have said, I don't think one unit with a dual purpose is a good idea. I have this unit placed directly beside my gas furnace and water heater. Then I have a dedicated CO detector in the bedroom.And as someone else said, the unit drains the battery while it is plugged in. Why? Who knows, but the battery must be replaced every few months.