Audio alerts, buzzers and indicators refer to a broad category of audio signaling devices.  Depending on their principle of operation they can be classified as magnetic, electromechanical, mechanical, electromagnetic, piezo-electric or electro-acoustic audio signaling devices. This classification is based on how energy is converted from one form to another to give an audio output. For instance, an alternating electric field causes piezo-electric audio indicators to compress or stretch. This compression or stretch is what we get as a sound. In the case of electro-acoustic audio indicators electrical energy is converted into acoustical energy, producing an audio signal.

Audio indicators and alerts are designed to give an audio output when triggered through one or more of the available methods. The output from these devices can be a beep, click, or a ring. Apart from their underlying concept, audio indicators and alerts are also commonly categorized according to sound level, frequency range, rated voltage, packaging type, and dimension.

Audio indicators and alerts have a wide selection of applications in various fields and industries. Typical uses include: alarm devices, electronic metronomes, timers, household appliances, annunciator panels, and user input confirmation applications. Audio indicators can take various forms such as buzzers, alarms, horns, and loudspeakers.