The answer to 'why is my carbon monoxide detector hot to touch' is that the detector may be malfunctioning or overheating. Carbon monoxide detectors can get hot to the touch if there is an issue with the internal components or if it is detecting high levels of carbon monoxide. This could be a sign that the detector needs to be replaced or serviced.
If your carbon monoxide detector is hot, it's important to take it seriously. Carbon monoxide is an odorless, colorless gas that can be deadly, so a malfunctioning detector could put your family at risk. You should evacuate your home immediately and call a professional HVAC technician to inspect your heating system and ventilation.