Levo-Lon
Guru
We slighly made 'skeleton' keys in metal work a school... a blank key shaped thing that definitely opened my dad's Marina. Didn't dare try it on any other car though.
Many moons ago a mate had locked his keys in his car. I suggested trying any other car key, but he told me how super secure his car's locks were, and reckoned he'd have to break a window to gain entry. I reiterated that trying any other key was worth a try... but he was adamant that it wouldn't work, and began snooping around the river bank for a suitable rock. Meanwhile, the second 'other' car key i borrowed opened his car.
I could get into an old car in under10 seconds with a bent welding rod.
The new cars are better at defeating this method.
Plus alarms ect.
If a thief wants it it's gone I'm afraid.