Or put 6 volts to it, and it sounds normal, then in all probability, it is a 6 volt siren. The other alternative, is to "bump" it with 12 volts, and if it takes off screaming, then you know it is a 6 volt siren. Third thing to try (but do it first), is to remove the front light, and see what voltage the flasher and the bulb is. Normally, 6 volt sirens used a 6 volt bulb and flasher. If the bulb and flasher is 12 volt, and the siren screams on 12 volts, someone used the 6 volt siren on a 12 volt system, and converted the light, to 12 volt.