A siren usually contains a Piezo Transducer and can emit a very loud wailing sound - typically 110dB+

They can be bracket mounted or directly screwed down.

Sirens generally operate between 6 to 12 volts with an average current around 100 to 250mA.

Sometimes a capacitor is needed across the supply to help the drive circuitry inside the siren function properly.

A standard Transistor Driver can easily drive most sirens. For larger types try using a Darlington Driver instead.