The answer to 'how to fix carbon monoxide detector' is to first check the batteries and replace them if needed. If the detector is still not working, you may need to clean or replace the sensor inside. This is a relatively simple DIY task, but if you are not comfortable doing it yourself, it's best to call a professional electrician to inspect and repair the detector.
Carbon monoxide detectors should be tested monthly and replaced every 5-7 years, or as recommended by the manufacturer. It's also important to ensure the detector is placed in the correct location, usually 5 feet off the floor, and away from windows, doors, and vents.