he term "source" here does not refer to the power source, but rather the oscillation source. That is to say, an active buzzer has a built-in oscillation source, so it will sound as soon as it is powered on. A passive buzzer, on the other hand, has no built-in oscillation source and cannot be driven by a DC signal. It must be driven by a square wave signal of 2KHz to 5KHz. Active buzzers are generally more expensive than passive ones precisely because they contain an additional oscillation circuit. This is how they can be distinguished by their driving principle.

Visual Differences

The two types of buzzers may look similar at first glance, but a closer look reveals a slight difference in height. The active buzzer has a height of 9mm, while the passive buzzer has a height of 8mm. If you place both buzzers with their pins facing upward, a passive buzzer will show a visible green circuit board, while an active buzzer will be sealed with black epoxy without a visible circuit board.

Difference Measured with a Multimeter

Use the resistance (R x 1) setting on a multimeter. Connect the black probe to the "+" pin of the buzzer and tap the red probe against the other pin repeatedly. If you hear a "click, click" sound and the resistance reading is only 8Ω (or 16Ω), the buzzer is passive. If it produces a continuous sound and the resistance is several hundred ohms or higher, the buzzer is active.

Additionally, an active buzzer will produce a continuous sound when connected directly to its rated power supply (the rated voltage is usually marked on the label of a new buzzer). A passive buzzer, like an electromagnetic speaker, must be connected to an audio output circuit to produce sound.

Advantages of Passive Buzzers

Lower cost

Controllable sound frequency, capable of producing musical tones (do, re, mi, fa, sol, la, ti)

In some special cases, can share a control pin with an LED

Advantages of Active Buzzers

Easy to control via programming