The answer to 'why is my carbon monoxide detector' is that your carbon monoxide (CO) detector may be going off for several common reasons. Carbon monoxide is an odorless, colorless gas that can be deadly, so it's critical to take a CO detector alarm seriously.
Some common causes of a CO detector going off include a malfunctioning fuel-burning appliance like a furnace, water heater, or stove, a blocked chimney or vent, or a vehicle running in an attached garage. Symptoms of CO poisoning include headache, dizziness, nausea, and fatigue. If your CO detector is sounding, immediately evacuate your home and call emergency services or a professional HVAC technician to investigate and resolve the issue.