More than a hundred incidents of GPS jamming in the UK were uncovered in the world's first investigation into the illegal practice.
GPS specialist firm Chronos Technology conducted the investigation known as Project Sentinel in conjunction with the police. The US-operated satellite navigation system is particular vulnerable to jamming given the extremely weak nature of the signal on earth.
That's why, compared to more common mobile phone jammers, GPS jammers are particularly nasty because a simple low-power transmission can block out GPS access for hundreds of meters beyond the intended effect.
The devices are often used by those with on-board GPS tracking hardware in their vehicle when they don't wish to have their exact location broadcast.