A Staff Report from the Straight Dope Science Advisory Board

Are car keys unique? Can you unlock someone else's car with your key?

June 5, 2000

Dear Straight Dope:

How unique is a car key? I only ask because: Most car keys I've seen seem to be generally the same shape, length, etc. Car keys wouldn't appear to have as many nook-and-cranny combinations as, say house keys do. Car ignitions can't be that sensitive, able to recognize microscopic differences from one key to another. Or can they?

Bottom line, how many cars do you figure it would take to find one that isn't yours that would open and start with your key?

Are they unique? No, but they're getting closer all the time.

I had a 1985 Toyota Corolla I could start and drive around using my pocket knife. Or a paper clip. I'm not sure if I'm bragging about this feature, but it did come in handy when I'd lost my keys, which was frequently. It was also handy for the people who stole the car.

A Volkswagen repairman told me once he took a customer's key out to the lot. The key fit in the closest bus so he brought it in and did the work on it before realizing it was the wrong bus. It was a 1968 model, so presumably they didn't have too many key combinations then. Or, like with my Corolla, it was more an issue of ignition sensitivity/wear than a key uniqueness deal. I also remember being with a guy once who tried his key in a parked car, the same make, model and year as his, and finding to our surprise he could unlock the door.

So I made some calls. How many possible car key combinations are there? After asking a few guys named Dave at key shops, locksmiths and auto parts places who said, "Oh jeez, gazillions," I found:

1) Bob at Bill's Keys in Albuquerque, New Mexico. Bob said how many different keys are possible depends on the automaker. I could hear him tapping on a calculator in the background before he came up with the figure 1,480,576 key combinations for GM vehicles and about 65,000 for Chryslers. He was adding/multiplying the different number of tumblers, depths and positions possible in those locks. Each lock/key has a code to set the key cutting machine.

2) Steve at Dave's Lock and Key immediately answered that there are only about 100,000 different possibilities to GM keys and about 5000 to Ford and Chrysler cars (why do I trust Bob with the calculator more?).

3) My buddy Chris who runs an auto junk yard (guy has a master's degree in English and inherited a junk yard--thanks, Dad) told me he thinks car keys are close to unique nowadays, but back in the 1970s his father kept a huge ring of keys on the off chance he could find one to fit.

4) Claude "Lock-Man" Hensley (http://www.lock-man.com/) said that generally the older the make of the car, the fewer combinations there were. Most 1981 and earlier cars had 5-6 tumblers and 4-5 possibilities for positions. Later many of those manufacturers went to 8 positions, and then to 10. That's why keys keep getting bigger and longer. The extra tumblers add many more possible combinations and therefore lessen the possibility of "crossover." The newer the car, the more different keys they can make for it. Guy signs his e-mail, "Lock-Man." Good enough for me.

You get the basic idea: there used to be relatively few key combos and now there are a shitload.

Bob at Bill's told me that some manufacturers are now incorporating radio transponders in a crystal in the head of the key. Yet another thing to give us brain cancer or, if you keep your keys in your front pants pocket, maybe worse. It's a "passive" transponder, though, and doesn't emit a powered frequency as you would find in a cell phone. Your car's computer looks for these transponders and if the ID code doesn't match, shuts down the fuel system within 15 seconds. Bob says there would be a minimum of a billion possible combinations for these keys. The downside for some of these newfangled keys is that you may no longer be able to call a locksmith to open your car when you're locked out of it. You'll have to call the dealer.

Apparently some of the new Toyotas or Lexuses (Lexi?) have a ECM computer and if all the keys are lost, the replacement cost is approximately $2900. If you don't believe me, call the Lexus dealer and tell them you lost all your keys to your 1999 Lexus ES300 or LS400 and see what they tell you.

Says Lock-Man Claude, "The intention of this security technology was not to keep the customer from driving his own car; but unfortunately that is what is happening to some. I have run across many a furious customer that resented they had not had it explained to them, if they lost their car keys they would have to be towed to the dealer."

One Dave at a key shop summed it up: "These guys are making our lives miserable."

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