To block GPS signal, it is much more difficult than just blocking a radio signal with basic radio interference. There are many places where we need to disable GPS device. If you were tracked by bad guy who put a GPS device in your car, do you want to block it? When GPS jammer has been created (specifically by the government, military organizations and spy or privacy gadget companies), most people do not have the technical capabilities to create their own home made device.
At the beginning, the GPS Jammers were built for military uses, for example, to confuse the enemy on where their exact location is or where the enemies GPS guided missiles or bombs will fall. However, in our lives, there are a few civilian uses for jamming GPS signals including the ability to conceal oneself or one’s vehicle in the case that it is being tracked by a GPS receiver.
Before we buy or use GPS signal jammer, it should be noted that most GPS jammers are illegal to build or use in some countries or localities due to the potential for misuse. For example, a GPS jammer can interfere the signal of aircraft and other vehicle instruments, possibly causing mishaps. Before you buy the GPS jammer, you should study the telecom and communication law of your country. Also, you should make sure you won't use it near any airport or harbour or other public facilities that use GPS system.