GPS Jammers Present Many Dangers
GPS jammers are used in potentially less harmful circumstances as well. In Germany, some drivers are reportedly using GPS jamming devices in order to avoid GPS-based road charges. Although it's illegal to sell or use these types of jammers in Germany as well as in the UK, the law isn't necessarily stopping people from doing so. Since a GPS jamming device that puts out approximately 2 watts is sufficient to disrupt a GPS signal in a vehicle that's within 10 feet of the device, it's conceivable that GPS jammers could be used to render stolen vehicles undetectable by law enforcement and other services such as OnStar.
For the military, GPS jamming devices present even greater threats. Some soldiers are using consumer grade GPS devices instead of the secure units provided by the military. These consumer grade devices are easily compromised by jammers, and the information could be used against the soldier carrying the unit, as illustrated in this video:
All is not lost, however. As the video also points out, there are secure GPS channels as well as unsecure ones. In addition, a system is currently in prototype stages in the UK that would detect jammers. Such a system could be deployed in airports, harbors, and other locations that depend on the accurate timing of GPS signals.