I haven't got one, but I like the idea of the GPS, tracker, disable devices you can get.
Like this one ... there are other makes ...
https://www.finditstopit.com/
I have fitted a couple of these
https://www.toadalarm.com/product/sterling-excel-immobiliser/ they are very effective and would take some time to bypass.
There is a wire loop fitted behind the plastic surrounding the ignition that you hold a fob against which allows you to start the car. Essentially it is a relay on the cuttoff switch and a couple of other components in the starting/ignition system.
Essentially it's a box fitted/hidden behind the clocks with about 10, identical, black wires, you'd really need to know a lot about car electronics to disable/bypass it.
Some have a relay that when tamprered with sounds the horn (or similar device)...