The use of motion detectors and motion sensors to detect ghost movement...
Motion sensors and detectors are another ghost hunting tool that some ghost hunters use during investigation. If used correctly, such devices can be strategically placed to let the investigator know if something is moving in another room, or from room to room, while the investigative team is elsewhere but nearby.
Motion detectors work well when left in a room during the time when no investigator is present, allowing the ghost to move more freely about the place. The detector should have an alarm that sounds when movement is detected in the room or doorway where placed. We found that the use of motion detectors helps when investigation larger homes and buildings, giving the ghost investigation team a broader area of coverage. Wherever the alarms go off, then, additional monitoring equipment can be placed in that location (such as a stationary video camera). We prefer using simple, portable motion detectors.
Some motion detectors will only turn a light on when motion is detected. These can be used in place of a chime or alarm-type sensor when an alarm sound is not desired, but investigators need to ensure they are not setting off the unit themselves if investigating nearby. If working near any motion detectors, we recommend testing the range, placing a colored masking tape line on the floor to act as a "do not cross" line.
Motion sensors used by ghost hunters project an Infrared beam. When the beam is disrupted by movement of any kind (natural or spirit), some sort of alert will sound so that the investigator can hear while away: a clue that spirit activity may be present where the motion detector resides. Usually motion sensors have an alarm mode and chime mode. The chime mode will only announce the visitor or movement but will not blare as a siren for a long time. Most ghost hunters prefer the chime mode setting on their motion detector, as it is less offensive and won't scare the dickens out of you!