Bluejacking is the use of Bluetooth wireless technology to either send messages or files to a phone, or connect to it in other ways. The benefit of Bluejacking is that the connection isn't conveyed through a carrier, so it's harder to track. And it's anonymous.

Bluejacking is easy. In fact, you can download Bluejacking software from the Google Play store, or from any number of other sites.

Some software lets you find "hidden" open Bluetooth connections. And you can typically send messages, pictures or even sounds.

Although Bluejacking is primarily used in sophomoric pranks, it can also be used for social engineering, which is one of the things the characters in Person of Interest use it for.