Update on the "microwave ray gun able to beam sounds directly into people's heads":

The device – dubbed MEDUSA (Mob Excess Deterrent Using Silent Audio) – exploits the microwave audio effect, in which short microwave pulses rapidly heat tissue, causing a shockwave inside the skull that can be detected by the ears. A series of pulses can be transmitted to produce recognisable sounds.

The device is aimed for military or crowd-control applications, but may have other uses.

...MEDUSA involves a microwave auditory effect "loud" enough to cause discomfort or even incapacitation. [Developer Lev] Sadovnik says that normal audio safety limits do not apply since the sound does not enter through the eardrums.

"The repel effect is a combination of loudness and the irritation factor," he says. "You can’t block it out."