Cell Phone Jammer
Cell phones (and phones is general) are annoying. Especially when people use them when/where they're not supposed to (hospitals, airplanes, movie theaters, office, etc.). This gadget will let you disturb the cell phone signals in up to 10 yards around you so that you can actually watch that movie or concentrate on your work. Sounds great? Well, a disclaimer here is that these devices are actually illegal in most countries, including U.S., and you might end up paying a huge fine (think $10k) or even go to jail. It might still be worth it.