Long before we ever used GPS to find our way around town, former FBI agent Rick Smith was using it to keep an eye on suspects.
"It's been used for quite some time, it was used when I was in the FBI 15 years ago, but it's, the technology has improved where the device is obviously much smaller," said Smith.
"Ten years ago I would say this was state of the art," said Jason Woodside.
Woodside, who owns the International Spy Shop, showed us an elaborate kit that once cost thousands of dollars and took hours to install.
"Today's trackers have gotten a lot smaller," said Woodside. They're small, easy to hide, and cost a few hundred dollars. "On a vehicle this size the spare wheel tire has a lot of metal on it, you can just reach in [he attaches the device] and you're good to go, no one can see it."
For private citizens, it's illegal to track a car without the owner's permission, but it's not for the government.
"It does not require a warrant in most situations," said Smith.
And that's where the American Civil Liberties Union comes in.
"If the government wants to be able to access and track our location through GPS devices, they need to go to a judge and get a warrant," said Nicole Ozer, an ACUL attorney.
The U.S. Supreme Court is considering requiring a warrant for GPS tracking. The ACLU says it would be a critical step to protect privacy.
"Many people might be thinking, 'You know, this Supreme Court case has nothing to do with me, the government will never be installing a GPS device on my car,' but the reality is that the government doesn't need to install a GPS device in your car to track you," said Ozer.
The fact is most of us already have a GPS device tracking our every move -- our cellphones. They're made by companies like Apple and Motorola and they report our location to companies like Verizon and AT&T.
CNET's GPS expert Antuan Goodwin says phone companies have plenty of legitimate and legal reasons for tracking us.
"They collect data for things like finding outages in their cellular coverage, you don't actually have to report these things now when you're in a dead spot, your phone is doing the reporting for you," said Goodwin.
But a Department of Justice Document reveals that phone companies store that information, sometimes for years.
"Do you remember everywhere you've gone since July 2008? You know, I don't remember this, but AT&T knows because I'm an AT&T customer," said Ozer.
"I can assure you that the industry goes to extraordinary measures to keep that information safe," said CTIA spokesman John Walls.
Walls acknowledged one reason for keeping that data is in case it's requested by police.
"They have to show just cause for that location information to be shared, they have to go to the legal system, go to a judge, provide the proof, and then get a warrant," said Walls.
"We know that Sprint received over eight million demands for location information in just a 13 month period," said Ozer.
And privacy advocates say while it's one thing to know somebody's location, knowing everywhere they've been for the past few years can tell you their whole life's story.
"GPS data can reveal where you live, what your child's school is, what doctors you visit, whether you go to a political protest or you go to a religious service," said Ozer.
But Smith insists, most people, have no need to worry.
"If you're not transporting 1,000 pounds of coke, you shouldn't have a concern," said Smith.