These piezo buzzes are perfect for hooking up to your flight controllers to notify you of battery voltage warnings and other audible tones for feedback from your multirotor. They are 12mm in diameter and appx. 9mm in height and have two pins for connecting wiring back to your flight controller. The pins have the polarity marked on the case of the buzzer, so make sure you hook up the + and – correctly so it functions as it should. These are 83db, and are plenty loud for most fpv racing multirotors.