NEW YORK (CNN/Money) - It's no secret that where you live has a huge impact on your car insurance premiums. That's why some people lie on insurance applications to keep their car's location a secret.

For example, if you live in Detroit it might be tempting to try to convince your auto insurer that you live someplace else. Actually, just about anyplace else.

It costs more to insure a car in Motown than any other U.S. city, according to research by Runzheimer International, a company that tracks relocation costs, including auto insurance premiums. A person living in Nashville would pay about 20 percent as much.

Sometimes, car owners are simply lazy about updating their information. "The most common type of that is people leaving their parents' home to go to college and never updating where they live," said Daniel Finnegan, president of Quality Planning Corporation, a company that performs data analysis for insurance companies.

Often, however, deviousness is involved. Some policy holders will go so far as to ask friends who live in cheaper-to-insure locales to take mail for them, said Finnegan, so that they can pretend to be living there and get that area's insurance rates.

Rather than trying to fake a different home address, other people will say that their car is garaged at a different address. In two-thirds of the cases where car owners tell insurance companies they store their vehicle somewhere other than at home, said Finnegan, the car costs less to insure than it would if it were kept at the owners' home address.

QPC's policy reviews frequently turn up addresses that are actually private post office boxes.

"I don't think the cars really fit in those little boxes," jokes Finnegan.

QPC's database reviews have recently turned up a number of cars across the country registered to addresses where the residents probably shouldn't be driving.

"We just uncovered a number of addresses that were prisons," he said.

It's not just insurance rates that make it tempting to register vehicles in places other than where they're actually kept and driven, said Bob Hartwig, chief economist with the Insurance Information Institute.

Differences in sales taxes and fees, combined with lower insurance costs, can also raise the temptation to fake a car's real residence.

"Added all up, someone can end up saving several thousand dollars on the purchase of a new vehicle," he said.

The downside, of course, is that the point of buying car insurance is to be financially covered in the event something happens to your car. If you lie on the insurance application -- thereby misrepresenting the risk you represent -- the insurance company might not have to pay you a dime.