Passive Infrared Motion Detectors are a useful tool for ghosthunters. They work great when left in a room during the time when no investigator is present. We have had them go off in rooms where no activity has been reported and upon further investigation, we found much evidence of spirit activity in the area. The motion detectors used by paranormal investigators Do NOT project an infrared beam.  They detect or receive the infrared heat signature off of anything that is above absolute zero. If the sensor detects movement in an area where there was nothing visible, the sensor has picked up something invisible to the naked eye that is giving off an IR heat signature. When in monitor or chime mode, the alarm chimes to announce movement and then stop. The models may vary and which model you receive may vary depending upon which is available to us at the time of your order. We have used all of these alarms many times and have gotten excellent results with each of them.