MEDUSA (Mob Excess Deterrent Using Silent Audio) is a device that uses microwave pulses to beam sound directly into someone's head. In development by the Sierra Nevada Corporation originally under a US Navy contract, MEDUSA can apparently fill your head with incapacitating "shockwaves" or possibly even whispered messages. From New Scientist:
(Researcher Lev) Sadovnik says the technology could have non-military applications. Birds seem to be highly sensitive to microwave audio, he says, so it might be used to scare away unwanted flocks.
Sadovnik has also experimented with transmitting microwave audio to people with outer ear problems that impair their normal hearing.