As a retired cop and a mechanic shop owner for 30 years plus wrenching for 45 years, I have found the easiest way to keep your car is to put in a kill switch. Find the wire going to the electric fuel pump in the gas tank. Then cut it and spice in a toggle switch. I put the switch next to the rear seat inside the door (sort of over the wheel well area). Then when I park, I get out, open the back door to take out something, drop my hand next to the seat and flip off the switch (and if somebody is watching they will never suspect you just turned off a switch). No matter what they do, they won't get the engine started and they won't find the kill switch either. Putting a switch near the driver is easy to find and circumvent. However, be warned, that when the thief gets frustrated and can take the vehicle, they may instead inflect damage on the poor vehicle. Just my 2 cents worth and anybody can do this themselves for about $5 in parts and 30 mo9ntes of time.