Many of the thousands of cars stolen each year would have remained in the possession of their owners if the owner had taken some steps to prevent the theft. There's no way to guarantee that your car won't be stolen, but there are things you can do to make the thief's job more difficult. Difficulty spells time, and time is something the thief doesn't want to take a lot of. LOCK THE CAR, AND TAKE THE KEYS WITH YOU. Strange as it might seem, many car thefts are made very easy because the owner left the keys in the switch. INSTALL SMOOTH DOOR LOCKS ON THE INSIDE. If your car has inside door locks -- the push-pull type that are mounted vertically near the window -- replace them with the smooth tubular type. This prevents the would-be thief from using a coat hanger to lift the lock up -- there's nothing for the coat hanger to catch on. Smooth door locks are available at auto-parts supply stores. To remove the old door locks, just screw them off and screw the smooth lock on. A professional theif doesn't much care whether you have smooth lock knobs or not, but this can deter an amateur. INSTALL AN EXTRA IGNITION SWITCH. Basically, this involves putting another switch in the primary ignition circuit so the car won't start when the ignition switch is turned to the start position.
This may deter even a professional: If the car won't start, he may not want to spend time looking for another switch. Installing such a switch is not a job for an amateur, but a mechanic can do it for you at relatively little expense. INSTALL A FUEL SHUT-OFF. This type of device prevents fuel from reaching the carburetor shortly after the engine is started. The engine then stops. In this situation, if the thief manages to get your car started, he may drive it away, only to have it stop after a short distance. Again, he may not want to take the time to trouble-shoot the car to see how he can make it go again.
Anti-thief fuel shut-off devices are available at various places that sell auto parts and accessories. Depending on your mechanical skills, you may or may not be able to install it yourself; having a mechanic install it is not super-expensive, though. INSTALL A BURGLAR ALARM. There are various alarms available in the $30 to $150 price range that can be installed by the average do-it-yourselfer. They come with installation instructions. Basically what they do is set off a siren (often mounted under the hood) when someone starts tampering with your car. These alarms are available at various places that sell auto supplies. TRY TO PARK IN A WELL-LIT AREA. Athief would prefer to work where he can't be seem easily.
Doing these things to your car greatly reduces the likelihood that you will walk out to it someday -- and find it gone.