How to make a siren from one speaker without transistors

If you suddenly need a loud siren for your homemade alarm system, then it can be very easily made from any available dynamic head.
You don't need any circuits or transistors, just the speaker itself, a pair of wires, a screw and a nut.

Making a siren from a speaker

So, take a long screw with a square nut. You can also use a regular nut. We take the wire, strip it and wrap it in a nut or screw, there is not much difference.

We glue it to the speaker body, to the magnet specifically, along with the wire. Two-component resin or “cold welding” are ideal for this.

Everything is installed in such a way that the bottom of the screw touches one of the flexible wires going to the diffuser.
Solder the second contact to the opposite terminal.

We connect a power source with a voltage of 1.5-9 V. A 3.7 V battery from an old mobile phone will do. Carefully rotate the screw until you hear a persistent siren sound.

The siren is working. If nothing works the first time, change the polarity of the power source.

How it works?

When power is supplied to the dynamic head, the screw touches the wiring, the circuit is closed, which means that under the influence of electromagnetic force the diffuser moves forward. As soon as this happens, it moves the wires away from the screw, which means the circuit opens. As soon as the power is lost, the diffuser moves back and closes the contacts again. So the cycle repeats ad infinitum. The frequency of sound depends on the size of the speaker and its resonance.