Note: You can't really use PWM to vary the volume of a buzzer. I think it has something to do with the oscillator. For example, at 192 (75% duty cycle) there is NO sound, at all.

Each buzzer consists of an Arduino Pro Mini 3.3 V, a nRF24L01, ... [Flute Systems] notes that the current version of the buzzer can’t actually recharge it.

Each buzzer consists of an Arduino Pro Mini 3.3 V, a nRF24L01, ... [Flute Systems] notes that the current version of the buzzer can’t actually recharge it.