I'm sure I saw this when it came out, but its a good hack. The glow from your monitor can probably be seen out of your window. If you slowed things down really slow it wouldn't appear as a glow, but rather a strobe, as the electron gun in your monitor sweeps across rows of phosphorus. If you recorded the flashes, and knew the rate at which the gun was sweeping, you could reproduce the image displayed on the screen. Nice...

Optical Emission Security FAQ