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. There should be a reset button on the CO alarm, you can also take the device to fresh air / outside, so the sensors resets itself, and bring it back inside. If the CO alarm sounds again its either improper calibration of the unit / faulty device which you cannot do anything about or there’s an elevated level of Carbon Monoxide gas inside your home.
Turn off any fuel burning devices in your home; open the windows to replace supposedly CO contaminated air with fresh air from outside and check if your CO alarm is still being activated. If it is quiet, turn on the furnace and other fuel burning appliances (you can do it one at the time to determine which one might be causing this behavior) and let it run for a while to see if it activates the CO alarm’s sensor again.
I would also recommend getting another Carbon Monoxide alarm just to make sure that both of them are responding the same way in your home. If this problem persists, don’t just disable the alarm and continune running your appliances; turn them off, open the windows / move to fresh air and call a professional to investigate and correct the problem. An HVAC contractor should be able to help you.