Detecting Motion with a PIR Motion Sensor

In addition to the IR problems below, the same group found themselves despairing when they got unpredictable results using the PIR motion sensor.

While some uses had yielded feedback of "motion!" and "no motion detected!", in most cases the device wouldn't stop claiming to detect motion, even when placed in a dark box.

I've figured out the answer, and I look forward to seeing the boys figure it out themselves. The key detail is in the very first paragraph of the main product page, right here, on Sparkfun's web site.