[kurthr]

The LED just reveals power (detection of radiation over many visible orders of magnitude) ... it doesn't need to detect coherent I/Q, because I don't think neural effects are sensitive to phase either. Selectively cooking a brain would require relatively high power and beam forming, but not high data rate. Audio frequencies are visible (use multiple band pass filters if you like) .

You'd also want a controlled test source so you'd know if the attacker had burned it out.