I was wondering after seeing a repeat of GHI about the motion sensors.  A light that looked like a flashlight "walked" around in view of a camera, and their evidence that it was a ghost was the motion sensor not turning on the light.  This reminds me of the lighthouse episode on GH when they filmed the ghost at the top with no light turning on from the motion sensor.

The motion sensor seems pretty simple, could you defeat it just by putting tape over the sensor?  Then you can film something moving infront of it "proving" it was a ghost.