Home made Immobizer??

[Altransit]

secrete a 110 db siren in the headlining just behind the robbers' head.......

I'm liking that idea ......... a lot

[sideshow_bill]

Wire the fuse of a http://chemistry.about.com/od/chemistryhowtoguide/a/coloredsmoke.htm smoke bomb into a circuit that if not disabled when the ignition is turned on?
Just make sure you dont forget!

[darkbluevanman]

You could always use a changeover switch in the starter trigger wire and secrete a 110 db siren in the headlining just behind the robbers' head....... Soon as it tries to start the siren.......dissuades the scrote and warns you!

This could be adapted to work in the stop solly wire.

I've got an 'in cab siren connected to the alarm, t'was a cracking idea but then realised you get all the chirps through it, passengers love it