As freshandminty's post.
Or back in the day I used to fit one of these.
Stick it between the battery -ve and the earth cable that bolts to it. Cheap as chips.
You might need to get a bit more clever if you want your clock to remember the time, or your radio to remember stations
But kill either the ignition circuit or the starter with it and you've produced an obstacle for some thieving barsteward.
Or back in the day I used to fit one of these.
Stick it between the battery -ve and the earth cable that bolts to it. Cheap as chips.
You might need to get a bit more clever if you want your clock to remember the time, or your radio to remember stations
But kill either the ignition circuit or the starter with it and you've produced an obstacle for some thieving barsteward.