http://www.alldatasheet.com/datasheet-pdf/pdf/14906/PERKINELMER/LHI878.html I got this thing to sense motion. But I can't completely tell how to use it. It seems one pin gets power, another ground, and another is parallel to the power and creates variances in the source voltage to be measured. But I cant tell which pins for which and how exactly to detect motion with the arduino. I figure I use a resistor to get the voltage down to around 2.5v so that the analog in can detect higher and lower voltages. But thats just a guess.