If you don't live in a city with a good mass transit system, you're one of the millions of Americans for whom a car is an absolute necessity. What do you do if you need a vehicle but you haven't got enough cash to put down or a good enough credit rating to get a decent loan?

For too many who fall into that category, the only legal option more often than not, becomes the 'buy here, pay here' car dealers who have no problem wheeling and dealing with customers who are perhaps 'credit-challenged'.

And increasingly, those dealers are equipping their vehicles with additional equipment the new owner knows nothing about... They're installing GPS systems that give them the vehicle's location for instant recovery if someone misses a payment. Is that legal?

The Tampa Bay Times reports that these devices aren't the kind you mount on the dashboard to navigate city streets. They're electronic locators, designed to help the repo man find your car if you stop paying. Some devices can even render the car inoperable until you pay up.

In the cat-and-mouse game between the late-paying car customer and the buy-here, pay-here dealer, the GPS locator is a new weapon.

But, the trouble comes when it's kept secret.

"They don't want the customer to know that if they don't pay, they can come find it," said Duane Overholt, an industry critic who runs the website stopautofraud.com.

Believe it or not, repossessions guided by GPS are so widespread the industry has its own trade group: The Payment Assurance Technology Association. The group has a code of ethics that requires its members to "fully define and disclose" the devices to customers. Of course, there are many times when that doesn't happen and lawsuits result.

Dave Ronsky, CEO of Ohio-based Payteck, said it doesn't even make sense to place the devices secretly.

"It's just good business to let the customer know that the dealer has the ability to either disable the starter of the vehicle or locate the vehicle," he said.

That way, customers know their payment isn't optional. "That's a more effective behavior modification tool," he said.

He requires dealers he works with to sign agreements promising to disclose the devices. Ronsky, like several others interviewed, said the devices are used in the "sub-prime" auto market. They're not going into Cadillacs or BMWs sold to people with good credit.

"It's the deep sub-prime, buy-here pay-here, consumers with poor credit scores," said Chris Macheca, CEO of Colorado-based Passtime.

The problem is, that practice is discriminatory. And legal experts say it may be illegal. Jon Mills, professor and dean emeritus of the University of Florida's Levin College of Law, said secretly placing devices raises "a lot of red flags."

Essentially what they're trying to do there is stalk the person," said Timothy Kaye, a law professor at Stetson University. "And you don't have a right to stalk anyone."

What do you think? Should car dealers be able to sell vehicles and track them and their owners without disclosing the practice?