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By Tom Krisher, AP Auto Writer

DETROIT (AP) — As the little computer inside your car key becomes more sophisticated, buying a spare is a good way to save money in case your key goes missing.

Newer cars won't start unless they read a signal from the key, making it difficult for thieves to hot-wire and steal your ride. But those keys also can be expensive.

Normally you get two sets of keys with a new car. Older vehicles, mostly before the mid to late 1990s, came with simple metal keys that you could duplicate at the local hardware store for a few bucks.

After that, automakers began making the keys bigger and installing computer chips. Keys had a separate fob, that dangling plastic device, to unlock doors or the trunk.

But more automakers are starting to combine the fob and the key, putting the unlock buttons on the plastic part of the key. And as the keys get more complex to stay ahead of crooks, they are becoming more expensive to lose.

Think it can't happen to you? Dealers and locksmiths say people frequently lose one, or even two of their keys. It can cost more than $1,000 to replace both on some models. So it's a good idea to get a third as soon as you buy a new car.

Here are three tips to save money:

Get an extra

Chip keys vary by make, model and years, but many automakers (mainly General Motors, Ford Motor Co. and Chrysler Group LLC) have a feature in which the car will automatically program an extra key if you have at least one, or sometimes two of the original keys.

It costs about $25 to buy an extra key from a dealer, locksmith or sometimes a local hardware store, and they duplicate the keys by cutting grooves in them, just like they used to. But here's where you can save money by getting the key early: The keys still must be programmed to match the signal to the car's computer. Dealers know how to do this. Some locksmiths also have figured it out on many models. But the programming can cost another $50.

On later-model Fords, for instance, if you put in each of your keys and turn the car to the "on" position for a few seconds (you don't need to start it), then put in the new key and do the same thing, the car will program the key automatically, said Greg Brandt, owner of Brandt Locksmiths in Kansas City.

"If you don't have three keys, you're leaving yourself open for some expense if you lose a key," said Jan Freudenberg, parts manager at Shults Ford in Wexford, Pa., north of Pittsburgh.

Which cars program keys themselves and how many keys you need to do that varies by model and make. It's wise to check with your dealer or a locksmith before spending any money.

The cheaper option

If you're prone to locking keys in your car, get a conventional metal key without a chip and have a locksmith or hardware store cut it to match your key. It won't start the car, but it will open the doors, and you can get in without having to call a locksmith or tow truck.

Protect your fob

Make sure you don't leave it in your pockets and run it through the washing machine. In most cases, that will fry the circuitry and you'll have to spend $50 or more on a replacement.

Since more automakers are integrating the fob into the head of the key, that makes it even more important to keep your fob out of the water. It can cost $110 or more just for a fob and key that are combined, and that doesn't include another $50 or so for programming.

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