Another alarm one
Not content with my car alarm just making a racket if you broke in, I decided to add my own "enhancements".

Output normally used to flash indicators routed to a delay timer.
After a few flashes, delay timer would switch on.
Delay timer fed another siren. A LOUD siren. INSIDE the car.
Delay timer also fed a step-up converter that kicked out 500 volts AC to wires conveniently placed on the bonnet catch. A thief can't shut the alarm up without opening the bonnet, but can't open the bonnet unless he shuts the alarm up, otherwise he gets a belt off it.

I never felt the full force of this nasty beastie (although I did get a taster of it when testing the circuit, thanks to a wet soldering iron sponge) but one of my mates did when I asked him to pop the bonnet when the alarm was going off :-)

The 500V power supply is still lurking in a box somewhere...
( eXOBeX, Fri 21 Aug 2009, 17:56, 3 replies)

You need to be careful
My old man is an electronics engineer, one of his colleagues used to own a sierra cosworth back in the day. Fed up with people attempting to nick it, he wired the body to an electric fence transformer (inverter?). He found himself in court after a traffic warden leant on it.

Although, my dad armed my mums' MG metro with 4 sirens under the drivers seat. It was bastard loud when the doors were shut :)
( Slippery Mick ‏, Sat 22 Aug 2009, 0:56, closed)

I remember reading a news article about something like that once,
May have been the same guy!

Mine only "had" you if (a) you'd set the alarm off and (b) you were trying to open the bonnet, so no warden zapping.
( eXOBeX, Sat 22 Aug 2009, 10:46, closed)

A friend of mine
did something similar with his house, wiring up a 130dB siren in each of the main rooms downstairs to the burglar alarm.

When he eventually was turned over, the police said that it was the first time they had seen evidence of a forced exit from a burglary.
( Amish Information Systems hates misplaced, commas, Sat 22 Aug 2009, 9:05, closed)