Complicated electronic systems make it difficult to access a circuit to prevent starting the engine.

After mine was stolen I fitted one of these

richbrook.co.uk/product/discarnect-battery-master-.../

Simple to fit and did what it said on the tin. Probably easy to spot if an experienced thief looked under the bonnet but since most simply work at the wiring under the dash that is highly unlikely.

When fitted with the fuse the small consumers keep working but any attempt to start the car will fail as the fuse will blow (I tried starting the car a few times when I had forgot to replace the knob - car did not start). Worth carrying some spare fuses and buying a spare knob.

was regularly ' borrowed ' and returned with a full tank, always knew it was in a slightly different parking spot!

That used to happen to me except returned with an empty tank - oh hang on that was my son!!

Back to the original question, years ago I fitted a battery switch to my kitcar with a red plastic key (+spare) - not sure it's a good idea with a modern car though unless it's just the live high current starter motor feed. I also designed a bespoke immobiliser that "read" the jaguar rocker switches (from xj6) on attempted startup - worked well for a year or so but discovered 74 series chips disliked the car environment and they started failing.

[EDIT] - switches still available:- www.amazon.co.uk/Isolator-Disconnect-Isolation-Eme...8

Edited by Big John on 28/03/2024 at 21:49

No definitely your fault these days, despite it being locked on a drive right under your window.

Do you mean theft reduces your NCD?

I'd expect that unless perhaps you'd paid extra to 'protect' it. Might also drive up the underlying premium as there are hot spots for theft.