The answer to 'my smoke detector won't turn on' is that there are several common causes, including a dead or disconnected battery, a faulty power supply, or an issue with the smoke detector itself. Smoke detectors typically run on battery power or are wired directly into your home's electrical system.
If the smoke detector is battery-powered, check that the battery is installed correctly and has enough charge. Replace the battery if needed. For hardwired detectors, ensure the power is turned on and the wiring is intact. If the issue persists, the smoke detector may need to be replaced, which is generally a DIY task. However, if you're uncomfortable working with electrical systems, it's best to call a licensed electrician to diagnose and fix the problem.