The Sentinel project, which has been running since January 2011, was designed to measure GPS jamming on UK roads. The project, run by GPS-tracking company Chronos Technology, picked up the illegal jamming incidents via four GPS sensors in trials lasting from two to six months per location. \"The idea behind Sentinel is to detect and locate interference,\" Chronos Technology\'s divisional manager Andy Proctor told ZDNet UK on Wednesday. \"Until you physically get a jammer in your hands you can\'t claim 100 percent it\'s a jammer, because you don\'t know what\'s been causing the interference.\" The Sentinel field trials of GPS jamming involved sensors in different locations. One sensor placed in a city next to some docks and a two-lane link motorway found 67 incidents of vehicles using GPS jamming over a six-month period, according to Chronos Technology\'s managing director Charles Curry. \"These events were real and corroborated,\" Curry told ZDNet UK at the GNSS Vulnerability: Present Dangers, Future Threats 2012 conference. GPS jammers work by broadcasting a strong local signal on the same frequency as GPS, effectively drowning the weak GPS signal broadcast by satellites. People illegally jam GPS for a number of reasons, Curry told the audience at the conference at the National Physical Laboratory. These include evasion of company-vehicle or covert tracking, and stealing high-value vehicles. In prior trials, a white van driver using GPS jamming had been apprehended by police, said Curry. The man, who was not brought to trial, was using jamming to evade company GPS tracking. ZDNet UK understands the man was apprehended as part of trials of GAARDIAN, a preceding technology to Sentinel. GAARDIAN trials ran from 2008 to 2011. Sentinel project Sentinel now has 20 sensors deployed in different parts of the country, Curry told the conference. The £1.5m Sentinel project is funded by the ICT Knowledge Transfer Network, and its partners include ACPO, Ordnance Survey, the National Physical Laboratory, the General Lighthouses Authority (GLA), the University of Bath, and Thatcham Security. Sensors tend to be deployed in premises owned by these organisations. From: Cnet