It is a federal offense. And yes, people have been caught, and the consequences were real.

　　How could radio interference be called “accurate?”

　　What a mobile signal jammer does is prevent reception of GPS radio signals. It does this by broadcasting noise. This noise extends quite a distance.

　　Blocking any radio signal is illegal in the US, EU and many other places.

　　The cheapest one would be a metal object. Place it over the GPS receiver/ external antenna and it will not get a fix. Although you would be traceable using the GSM network.

　　Thus a combination of GSM jammers and metal plates would be effective.

　　Although i would not advice the above as any tampering to the device can be traced by the installer.

　　 Yet they're easily bought online, and their proponents say they should stay that way. Was able to buy GPS jammers for as little as $50 from numerous online sources. He said GPS jammers could pose a potential risk if used negligently.