In its endless inventiveness, the US military has produced an "active denial system" disguised as a cross between a Transformer robot and a microwave oven. The system, as you've doubtless seen on TV, sits on the back of a Humvee and beams millimetre wireless waves at hapless punters. They yelp with dismay, as well they might - the beam reportedly feels as if you're being stroked with a blowtorch. But it does no harm, says the US military, and given their track record in harm and its causation you may be minded to trust them.
Death rays are all jolly good fun, and the revelation has been widely broadcast. But there are a couple of minor points that may yet entertain us further, even if we pass over the advisability of cooking people on the hoof.
The device is a powerful transmitter hooked to a large dish antenna. To create a tight beam at the frequencies it uses, that dish has to have a very precise geometry and be delicately aligned. How well either aspect will survive the broiling mob remains to be seen, but a well-aimed brick - or a sootbomb, or a handful of chains - could cause a lot of fun. That would have a number of effects: a lot of the radio power would hang around the vicinity of the operators instead of pootling away as planned, and that might not count as a good hair day. Also, if the antenna's mangled, a lot of the power could go back down the pipe into the transmitter. Transmitters don't like that - if they're well designed, they swiftly shut down; if they're not, they break; if they're badly designed, they go bang.
Ah yes, reflections. A dustbin lid, held as a shield, could plausibly bounce the beam back. It might not be accurate enough to hit the transmitter, but there'll be plenty of other forces of Laura Norder in the vicinity to play with. And a fine mesh woven into clothing, gauntlets and worn as a beekeeper's veil, should shield even the active rioter from the beam's basilisk glare. One could even design a baseball cap-like hat with a veil held up around the rim by a deployment device that automatically activates when the weapon's detected. And as for tin-foil burkas. Well.
And will it work in the rain? The US military has a poor track record here: stealth bombers that aren't stealthy when wet and cruise missiles that get lost if it snows are two fine examples. And let us not forget the legendary - possibly even true - encounter with microwave ovens in Yugoslavia which left NATO feeling severely underdone.