I purchased a few of these PIR sensors on ebail for $4.50 (USD) each. They took a while to arrive from you all know where but they seem pretty cool. I am planning to add them to my sentry robot project at some point. I bench tested them and they seem too work just fine off the EZB using a single Digital port. +VCC, GND, signal. device trips high when motion is detected.
Pyroelectric Infrared Module (PIR)