Interesting wireless Proximity Sensor

Interesting prox sensor build.  It uses an atiny, prox sensor, and RFM12B RF transmitter for the build.  The article figures the cost for each one to be around $15.  How I don’t know (atiny board $10, transmitter $5, sensor $3, battery connector 25 cents).  I’m thinking at least $20.  Still its pretty cheap in the end.

http://hackaday.com/2013/11/18/a-truly-wireless-motion-sensor/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+hackaday%2FLgoM+%28Hack+a+Day%29