The electromagnetic buzzer has its own oscillating circuit, which can make a sound when connected to a direct current. We also call it active buzzer that who has it’s owm oscillating circuit. Magnetic buzzer sound pressure level around 85dB, operating voltage at 1.5-24VDC, current consumption less than 30mA and the frequency is around 2700Hz.
The four parameters mentioned above are very important for choosing an electromagnetic buzzer. You must find out when you buy it, otherwise it is very likely that the product you bought cannot be used normally.