The buzzer is a very old technology with some significant virtues.
The buzzer is really old in terms of what the electronics industry has to offer today by way of noise makers, but having been around for decades, there are a lot of them “out there” in the field so a look at their operating principle is worth spending a little of our time.
A buzzer is built very much like an electromagnetic relay, but coil activation is controlled differently, as seen below.
In part 1 of the image above, the armature is being pulled to a resting position by a spring (not pictured here) at which position it has just arrived and before magnetic attraction from the coil has had its effect on armature position. The arm of that armature may even be curved a little bit like a deformed flat spring.
In part 2 of the image, the armature is being attracted toward the energized coil. The flat spring may get straightened out but the contacts are not necessarily separated yet, which means that the coil is still energized.
In part 3, the armature has moved toward the attracting coil and the contacts have opened up, thereby de-energizing the coil, which now is no longer an attractor. The armature then falls back to the part 1 position and the whole cycle repeats itself over and over again as shown below.
Buzzers have some significant advantages over more modern noise makers. They are mechanically rugged, they can function over very wide ranges of temperature, there is no radiation susceptibility, electrostatic discharges mean almost nothing, electromagnetic interference immunity is virtually infinite, and when properly coupled to the right acoustic environment, these things can be made loud enough to really command your attention.
John Dunn is an electronics consultant, and a graduate of The Polytechnic Institute of Brooklyn (BSEE) and of New York University (MSEE).