Some REM Pods also come with Ambient Temperature Deviation Detection (ATDD). If the temperature surrounding the REM-POD noticeably increases or decreases, the REM-POD will alert you.
The theory goes, that if a spirit moves near the device, it will go off. Ghost hunters and paranormal investigators use REM Pods to alert them to the presence of a spirit in the room being investigated. You may also hear investigators asking spirits to move toward the device in order to make the presence of the spirit known.