Hey want to hear a really loud noise? Apply 3V to 5V to this buzzer module and you'll be rewarded with a loud 2KHz BEEEEEEEEEEEEEEEEEP. Unlike a plain piezo, this buzzer does not need an AC signal. Inside is a piezo plus the driver circuitry that makes it oscillate at 2KHz. On one hand, that makes it really great for integrating into projects because you don't need an oscillating control signal. On the other hand, you cannot change the frequency.

Buzzer 5V - Breadboard friendly (6:25)