GPS / Gsm Real-Time Signal Jammers

Don't get too reliant on that GPS receiver, Magellan, since companies are now starting to release devices that locally block GPS signals. Detectnu's device not only block GPS signals within a 50-meter (164-foot) radius, but also GSM cellphone signals in a 20-meter (65-foot) radius. Another such device the CS-JG004 GPS jammer from Radixon Hadrian-blocks GPS signals in a 50-kilometer (31-mile) radius. Now, I can completely understand cellphone jammers (hint: people have no concept of tact in New York City and love to yap about God knows what quite loudly) , but blocking GPS? What good does that do, other than give mischief makers a rise?
Ok, so Radixon Hadarian claims that the device can be used to thwart GPS-aided terrorist attacks. Yes, and I'm Jack Bauer. Let's leave the crime fighting to the professionals and not to gadget geeks. -Nicholas Deleon