This circuit was obtained from an English magazine from 1980, but as it uses components that can still be found on the market, it can be easily assembled today. The circuit produces an audio tone that is amplified by the transistor. The NPN transistor can be a BC548 for power up to 9 V and at 12 V use a BD135 for higher power. For unijunction a 2N2646 can be used.
