Piezo buzzers are used for making beeps, tones and alerts. It's a great way to provide user feedback for your project.
The buzzer that comes with the MetaWear Kit is small and loud but you can find any buzzer that suits your project on digikey or sparkfun.
Keep in mind that some buzzers require a 1kOhm parallel resistor and some do not.
You can drive the buzzer with a simple 3-30V peak-to-peak square wave.
The buzzer is 13.70mm in diameter and 4.00mm thick.
To use, connect the red wire pin to power on pin 11 (3V) and the other wire (blue or black) to pin 10, the haptic driver pin on the MetaWear. Then connect a 1KOhm resistor in parallel (between pin 10 and 11) For the loudest tones, stay around 4 KHz, but it will work at frequencies between 2KHz and 10KHz. The duty cycle is always 50%.