Personal Alarm

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These handheld piezo screamers are also known as rape alarms. They are a very loud siren.

This one is particularly loud even though it runs on only two AA batteries. It uses a push-pull transformer output. This unit was manufactured with the 10K resistor at pin 4 instead of pin 3 due to a PCB layout error:

Circuit Diagram aka Schematic reverse engineered from circuit board

The transformer is very small:

Transformer

Safety, accuracy and completeness of information provided herein is not guaranteed,
so be inspired by it but do not use it as a basis for experimentation or other actions.

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