Active Buzzer

An active buzzer contains its own oscillator, so applying DC voltage produces a tone immediately with no code beyond digitalWrite HIGH. That makes it the simplest possible way to add an audible alert to a project. The trade-off is that the tone is fixed: you can control when it sounds and for how long, but not the pitch. If you need melodies or variable pitch, use a passive buzzer instead. Sounds with a single digitalWrite, no timing code needed; Loud enough for alarms and alerts; Very low cost and easy to drive; Compact through-hole package