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This one is weird enough that two separate references were necessary:

Wired: The Microwave Scream Inside Your Head
ABC News: Microwave Ray Gun Controls Crowds With Noise

Go read both before continuing here.

Now, I think we can all agree that this is both bizarre and terrifying, where by "all" I need to exclude the nice folks at ABC news. For some reason Mr. Hambling includes worries that a high power version might either not be feasible or might cause neural damage, but ignores the aspect that should rightfully terrify every law abiding citizen anywhere: a low power version could beam voices/instructions/advertisements directly into our brains, potentially at a level where they could subliminally influence our behavior. Anyone who thinks that corporations and governments won't take advantage of this is probably already a test subject, or just hasn't been paying attention.

Now you'll need to excuse me for a bit as I need to go make a tinfoil hat.