Here is an AWESOME SIREN for your model Police cars. There are 4 sounds, Wail, Priority, Phaser, and combination of the 3 sounds with air horn. The speaker is 36mm diameter, Circuit Board is 20mm square by 10mm high. A momentary switch is wired 7.5" from the circuit board. Press the switch once for the 1st sound, again for 2nd, etc. 5th press turns it off, or it will turn off automatically after 2 minutes of operation.
The speaker is about 7" from the circuit board The 2 power leads connect to a 9 volt DC battery source and the leads are 6" long. The power leads are color coded red and black for +/-. All you have to do is hook this up to a 9 volt battery, no additional electronics required.