Court decisions have been split on the legality of police using GPS devices to track the movements of suspects without a court warrant. Currently there are no laws that regulate the use of the Global Positioning System in criminal investigations. A 2006 National Police Agency directive tells police forces nationwide they can use the devices when urgent action on a crime is required and other means of trailing the suspects aren't feasible. But the Nagoya High Court judged in June that the warrantless use of such devices to investigate a serial theft case was illegal because it violated the suspect's privacy.
The high court went on to warn that the threat to the privacy of people under criminal investigation from the use of GPS devices will increase with further advances in the technology — and called for new legislative action to resolve the problem. Relevant parties should take the warning seriously and start discussing legal controls on the use of GPS in investigations.
GPS is indeed a useful tool for police investigators. The police rely on the positioning service provided by a major security firm using the GPS system. Investigators secretly attach a rented device to the underside of suspects' vehicles. They can then monitor their locations on a map by accessing the security firm's server with their cellphones.