Q:I bought a used 2002 Mazda Millenia, which came with only one key. I would like to get a spare key but it's a special blank. I tried one hardware store plus a locksmith. Both said they could not do it. Where can I get this done - for a reasonable price? - Tom G., Minneapolis

A:Locks are a funny invention. They're certainly useful, having reduced the barrier necessary to exclude an intruder from the size of, say, a long stone wall, massive wooden gate, or wide, deep moat, to a little device you can carry around in your pocket - or fit in a door or ignition switch. Instead of a long ladder, catapult or battering ram, you need only a little piece of steel to gain access for yourself, while excluding everyone else.

The system is not perfect, however. With enough time and ingenuity a determined thief can overcome any security measure. And that's good for novels and movies. Make the lock so difficult to circumvent that the typical thief would give up and move on and there's still a drawback, even compared to history's early barriers. It's hard to misplace a catapult. Root around the castle grounds for a few minutes, at most, and you'll stumble upon it if your wicked brother hasn't sold it for grog money. Not so with a key. That wonderful lock that's nearly impossible to pick becomes a moat-sized hassle when the little metal advantage you had over all thieves is suddenly not in your pocket. Or on the dresser. Or on the hook in the closet. "Honey, have you seen ... ?"

And so it is that we make more keys, doubling, tripling, quadrupling the odds that one will fall into thieves' hands because being locked out of our house or car is just too annoying to bear in our hurried world. How many million dollar homes with a first-rate lock have a fake rock ten feet from the front door with a key underneath?

A spare key is peace of mind, yet making it hard to duplicate is one more way to discourage theft - such as by the parking valet who would like to park a beautiful $80,000 Mercedes, then run to the hardware store and get a key made for a later joy ride or black-market sale.

Your Mazda Millenia key is often called a "laser-cut key," but the locksmith I spoke to said it is not actually cut with a laser. It does require a special cutter, though, which the typical hardware store or department store would not have. Some keys of this sort are "transponder" keys, which have a chip and involve programming. There are more steps in duplicating and making effective a key of that sort. The Mazda Millenia key, however, is not of the transponder type. Thus all you need is the correct blank.

The shop I spoke to (I have not used and am not in any way connected to this shop) is Minneapolis Lock & Key (612-823-8148), which said they can make a duplicate of a 2002 Mazda Millenia key for $25. My research suggests that for this key, that's a pretty good price. Feel free, of course, to call some further shops for perspective.