It's pretty obvious why a paranormal investigator might consider setting up motion detectors in an allegedly haunted location. People have witnessed apparitions walk through walls, vanish into thin air, and move from one level to another in a matter of seconds. It's a pretty accepted notion among paranormal enthusiasts that spirits are capable of moving from one place to another pretty quickly and most of the time, unseen. Since it's not possible for a living human being to be everywhere at once, the use of motion detectors makes it easier for the investigator to know if movement has occurred in various sections of a given location. In fact, the Paranormal Research Society uses motion detectors extensively.

While motion detectors, like most paranormal equipment, cannot recognize and prove the existence of paranormal activity, they do offer benefits to the investigator. Infrared radiation detectors watch for movement that generates heat. The greatest benefit is that movements can be monitored in many parts of a location simultaneously.

Some of the things that motion detectors might pick up are the movement of objects by seen or unseen forces, moving shadows, animals, people. It's easy to see why motion detectors are especially helpful in larger locations. Some investigators also experience paranormal activity where motion detectors are in use and the detectors do not catch anything. This is especially interesting when investigators witness movements of shadows or figures with their own eyes in the vicinity of a motion detector. Therefore, the use of this type of equipment for catching spirits and not catching them in conjunction with personal experiences can be equally important for evidence gathering.

Motion detectors start around $15 and go up from there in price. There are all kinds of detectors: pet-immune, microwave and infrared, sunlight-immune and more. They can be purchased for mounting on walls or ceilings or for standing alone. Many announce motion simply by chiming or sounding an alarm. Some include video or digital cameras so that the movement being registered could potentially get caught on film or in a photograph.