Motion sensors and detectors are another investigation tool that many ghost hunters use. Simply put, motion sensors or motion detectors are used to let the ghost investigator know if something is moving in another room, while the investigator is elsewhere. Motion sensors work well when left in a room during the time when no investigator is present. Motion sensors have alarms that sound when movement is detected in the room in which they are placed. Typically, they will sound in rooms where no previous activity had been reported; and upon further investigation, one may find much evidence of paranormal activity in the room where the motion detector or sensor sounded its alarm. The motion sensors used by ghost hunters project an infrared beam. When the beam is disrupted by movement of any kind (natural or spirit!), an alarm will sound that the investigator can hear while in another room: a clue that spirits may be present in that area 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!