Good topic Diabando!
My 1972 Mk1 Escort has a battery isolator cut into the battery cable, with the switch hidden
somewhere on the car. The benefits are that [1] the idiot thief will assume the battery is flat and give up, and [2] if I have any electrical gremlins, I can disconnect the battery from inside the car in a second.
My second device is a little more complicated, but also has two facets. It's a brake line-lock; the type used by drag racers to hold the front wheels for 'Marcus' type burnouts!!
When I park the car up, I depress the brake pedal, activate the lock and hold the front brakes, and the very clever thief (Well, he did get past the battery isolator!) will find the car won't move. Hah!! It also doubles as an effective way of holding the car on a steep incline with all four wheels locked. (It's rear wheel drive.)
My third is remote central locking linked to an electronic voltage-sensing alarm, and with the external door lock barrels deactivated.
They can't get in the car because the doors won't open due to deadlocks, but if they do (by smashing a window) the cabin pressure sensor and voltage sensors will activate.
Finally, I have an immobiliser that not only kills the ignition voltage supply, but also the starter solenoid feed, the headlights (as most thefts occur at night) and the electric fuel pump supply feed.
...And in addition to the above, I keep it in a garage and my dog sits and watches the driveway for intruders 24 hours a day!!
They ain't getting my car!!
