Police are increasingly using Global Positioning Systems to track and catch criminals.
    
The technology uses satellites to map out locations and police say it is more effective than trailing a suspect with officers.
    
For example, Wisconsin investigators shut down a drug operation after secretly planting a GPS on a drug dealer's borrowed car.

But critics say the technology goes far beyond surveillance and in some states, officers do not need search warrants to use the trackers.
    
Courts across the country are now trying to sort out whether law enforcement can continue to use GPS tracking systems without a warrant.