From the MAKE: Flickr pool

Tom is designing a breath transmission system using a PC case fan as a optical interrupter –

“Breath” is a breath-over-IP phy2phy system. You blow on one fan (anemometer, whatever you want to call it), that data is sent over IP to the other side where a fan it turned on to match how strong you are blowing on it.

Once a fan’s internal coil is removed it’ll spin freely, making it a suitable for measurement/interruption. Read more of his development process here – Opto-interrupters for Breath

IR emitter/detector pair and fan on Flickr

Blow Up – Breath amplifiers