The answer to 'smoke detector not working' is that there are several common causes, including dead or disconnected batteries, a faulty sensor, or an electrical issue. Symptoms may include the detector not beeping when tested, no lights or indicators, or the detector not responding to smoke.
First, check the batteries and replace them if needed. If the batteries are fine, the issue could be a malfunctioning sensor or other internal component. In this case, the smoke detector will likely need to be replaced. If the issue is with the home's electrical wiring, you may need to call an electrician to diagnose and repair the problem.