WattMote: Moteino/SY310 photo-reflective-sensor water-meter
EE-SY310 photo reflective sensor breakout board with Moteino wireless node. This sensor can be used to read a water meter or even analog electic meter dial (that has a black stripe on it). It is a DARK-ON sensor, it outputs a digital HIGH when it detects a light-dark transition.
See this video for it in action: www.youtube.com/watch?v=MErKTQ3HG1c
Write up here: lowpowerlab.com/blog/2013/02/02/meet-the-watermote-motein...