Buzzer and Bleeper

These devices are output transducers converting electrical energy to sound. They contain an

Buzzer (about 400Hz)	Bleeper (about 3kHz)
circuit symbol

internal oscillator to produce the sound which is set at about 400Hz for buzzers and about 3kHz for bleepers.
Buzzers have a voltage rating but it is only approximate, for example 6V and 12V buzzers can be used with a 9V supply. Their typical current is about 25mA.
Bleepers have wide voltage ranges, such as 3-30V, and they pass a low current of about 10mA.
Buzzers and bleepers must be connected the right way round, their red lead is positive (+).