Multi-tone siren alarm circuit

Here is a simple schematic diagram of a multi-tone siren alarm circuit. This multi-tone siren is effective for reverse horns, anti-theft sirens, and many other sirens. It produces five different tones that are more engaging than a single-tone siren.

The circuit is built around the well known CMOS IC 4060 as oscillator cum divider and the small audio amplifier chip LM386. IC 4060 is used as the main part of the polytone generator. A 100uH inductor is used at the input of IC 4060. Therefore it oscillates in the RF range of approximately 5MHz. The IC 4060 itself separates the RF signal into the AF and ultrasonic ranges. Audio signals of different frequencies are available at pins 1, 2, 3, 13 and 15 of IC 4060 (IC1). These multi-frequency signals are mixed and fed to an audio amplifier assembled close to IC LM386.

The output of IC2 is fed to the speaker via capacitor C9. If you need louder sound, please use the TBA810 or TDA1010 amplifier circuit.

Only five outputs of IC1 are used here because the other five outputs (pins 4 to 7 and 14) generate inaudible ultrasonic signals.

You can assemble the circuit on a common printed circuit board (PCB) and package it in a suitable cabinet. A regulated 6V-12V (or possibly a battery) can be used to power the working circuit.