The answer to 'why is my smoke detector buzzing noise' is that a buzzing or chirping sound from a smoke detector is typically caused by a low battery. Smoke detectors are designed to emit an audible warning when the battery is running low, alerting you to replace it.
Other common causes of a buzzing smoke detector include a malfunctioning sensor, a wiring issue, or the detector simply reaching the end of its lifespan (usually 10 years). In most cases, replacing the battery or the entire smoke detector unit should resolve the issue.