The answer to 'why is my carbon monoxide detector not working' is that there could be several common causes, including a dead or disconnected battery, a sensor failure, or a problem with the wiring. Carbon monoxide detectors are designed to alert you to the presence of this odorless, colorless gas that can be deadly in high concentrations.
If your carbon monoxide detector is not working, first check the batteries and replace them if needed. You should also test the detector by pressing the 'test' button to ensure it's receiving power and responding properly. If the detector still doesn't work, it may need to be replaced, as the sensors can fail over time. In some cases, the wiring connecting the detector to your home's electrical system could be the issue, which would require an electrician to diagnose and repair.