The answer to 'why is my carbon monoxide detector hot to touch' is that a hot carbon monoxide detector is often a sign that it is functioning properly. Carbon monoxide detectors use a sensor that heats up when it detects the presence of carbon monoxide gas, which indicates the device is actively monitoring for this dangerous gas.
However, if the detector feels unusually hot to the touch, it could also be a sign of a malfunction or issue with the device. This could mean the sensor is overheating or there is a problem with the internal components. In this case, you should contact the manufacturer or a professional electrician to inspect and potentially replace the carbon monoxide detector.