Car theft can ruin your day. Here's a nightmare: you walk out of the house, car keys in hand, ready to head off for a round of golf, a trip to the store, a weekend visit to the grandchildren, your job. You look at the spot in the driveway where your car should be, thinking "What's wrong with this picture?"

Finally the penny drops and the empty place has a name. Grand Theft Auto. You're a victim of one of the commonest crimes in the U.S.

The good news is that the number of car thefts in the nation has been dropping for four years straight. By the end of 2007 (the last year for which we have statistics), auto theft was down 11% from 2000 levels.

Still, none of that is much consolation when you're standing there staring at your empty driveway or parking place. So how can you keep yourself from becoming a statistic, another victim on car theft, and keep your car?

Think of car theft protection in "layers." Let's start with the top, most basic layer and move down to the more sophisticated and techie layers.

Prevent Car Theft, Lock It:

The first, and most obvious, layer is to use your common sense. The car door has a lock and you have the key. Always lock your car and take the key with you. No financial layout required.

Alarm it:

If your car has an alarm device--whether it's a screaming banshee audible alarm or a blinking, flashing visible alarm--use it. Thieves don't much like the kind of attention warnings bring to them. Like cockroaches, they'll run from the light. So always turn on the alarm system before you lock and leave. And keep your baby off the most stolen cars list.

Kill it:

Remember this: if a thief can't start your car, he can't steal it, or at last he can't take it very far. Look for a car with a kill switch, automatic fuel cut-off or smart keys. They'll make car theft more trouble than it's worth.

Track it:

When shopping for a new car, look for one with a built-in tracking device. It might be a GPS-based system, a radio frequency tracker or a system offered by a subscription service. Any of them will give police a way to track down your stolen car and retrieve it before its heart is cut out and sold upriver.

Use your head, use the tools available to you and the chance that you'll be a car theft victim will go down considerably.