WASHINGTON (CNN) -- It's the stuff crime movies are made of: Determined police officers shadowing their suspect as he drives around town, watching and waiting for his next move, always careful not to lose him.
David Lee Foltz Jr. faces trial on abduction and sexual battery charges after police tracked him using GPS.
But now, investigators can track a potential bad guy without ever leaving their desks, thanks to the Global Positioning System, or GPS.
The technology is easy to use and the devices are hard to detect.
All police have to do is attach a GPS receiver to a suspect's car and they easily go along for the ride online, tracking the individual's exact location in real time from their computer.
"I think it's a good use of resources. It doesn't put any officers in danger, which is a good thing," said Mike Brooks, a CNN security enforcement analyst and a former Washington police detective.
"You can sit at a computer and find exactly where [a suspect] goes."
But because investigators often track without a warrant, privacy advocates say the tactic threatens to monitor innocent people as well. Watch the debate over police using GPS »
"Law enforcement has a legitimate right to try to solve crimes and track suspects, provided that there are protections so that the innocent are not improperly snooped upon," said Norman Reimer, executive director of the National Association of Criminal Defense Lawyers.
He wondered how many people would be comfortable knowing that police could attach something to their car and be able track their whereabouts 24-hours-a-day, seven-days-a-week.
A recent case illustrates how investigators use the technology.
Court documents show Fairfax County, Virginia, police followed David Lee Foltz Jr. without a warrant in February by placing a GPS device inside the bumper of his van. See how GPS works »
Police began watching Foltz, who had previously been convicted of rape, after 11 attacks on women in the area where he lived, The Washington Post reported.
Foltz is facing trial, charged with abduction and sexual battery. He is charged in connection with an attack that happened after the monitoring began, according to the Post.
The attacks stopped after his arrest in February, the newspaper reported.
Foltz's attorney tried to get the GPS evidence thrown out of court. Chris Leibig wouldn't discuss the case with CNN, but said the tracking constituted illegal search and seizure, a violation of his client's Fourth Amendment right.
"Our main point with this is that before installing a GPS tracking device secretly on someone's vehicle, a judicial officer should make the decision about how much evidence is good enough, how long the tracking can be for, and the parameters of the tracking," Leibig said.
"I want to point out it's very easy to get a warrant if the police have a good reason, it doesn't take a long time, and if there is a real reason, the warrant will be granted."
Leibig described GPS tracking as more intrusive than just an investigator following someone down the street.
"It's a lot more like a police officer tagging along inside your car, an invisible police officer inside your car," Leibig said.
Despite Leibig's motion to suppress, a judge has allowed the evidence to be used at Foltz's trial this October, The Washington Post reported.
Police involved in the case would only say there is an internal review before GPS tracking can be used. Many privacy advocates say that's not enough.
The Supreme Court has yet to address GPS tracking without warrants, so the legal standards vary from state to state. Most allow it or haven't ruled on it. Courts in Washington and Oregon, however, have ruled police need a warrant before using GPS.
"It's a wonderful tool for law enforcement," Reimer said.
"The question always comes down to how much are we willing to give up in freedom and privacy for how much marginal increase in our security."