What is GPS jammer?
Seriously though, blast a signal at them that they're 2km above where they should be, and they'll drop like rocks out of the sky.
Chinese shipping thieves use them to throw off officials looking to track their freighters. It's weird, and dangerous for everyone not using it, as it messes up all the nearby GPS devices when used. Some have speculated that it was developed as a Russian cyberweapon. But, it's now used for other nasty stuff also.
(post is archived)