An active buzzer will generate a tone using an internal oscillator, so all that is needed is a DC voltage. A passive buzzer requires an AC signal to make a sound. It is like an electromagnetic speaker, where a changing input signal produces the sound, rather than producing a tone automatically.
To identify them, if you apply a DC voltage to them and it buzzes, it’s an active.
As far as commands go if you want to control the pitch, you would need a passive buzzer. PWM on the Arduino can be used to control the pitch and the volume at the same time (which may or may not be what you want). If you wanted to change just volume or just pitch I suppose some external circuitry would be required to change the amplitude without changing the voltage, and vice versa.
Active Buzzer Module
Passive Buzzer Module
About Sticker on Active Buzzer
Active buzzer module has a sticker on it which says “Remove Seal After Washing”. This seal doesn’t mean you are supposed to wash this buzzer..!!
The industrial PCB assembly process usually leaves residues — mostly soldering flux — on the circuit board. One step in the process is to wash the board (by dipping or spraying) with a solvent to remove those residues for long-term reliability and for the sake of appearance.
Active Buzzers have a openings for their functioning, and their performance would be adversely affected if the solvent or the residues got washed into the opening and lodged there. Therefore, such devices often have a sticker that covers the opening(s) that should not be removed until after the washing.
Removing the stickers adds an extra step to the process, so for really high-volume manufacturing, it is often worthwhile to select parts that are declared “washable” to begin with.
You can leave it on for a quieter buzzer – and a different frequency. Or remove it for a much louder buzzer plus get the tones intended in the software. (Move your finger around partly covering the hole while a buzzer is running and you will see the many frequency shifts caused by changing the acoustics). They also keep out dust and critters. A lot of Chinese manufacturers leave them on, maybe not knowing what it says.
