This emf (Electro-magnetic field) detector is the most widely utilized meter for ghost hunter's and paranormal investigators.
This devices can pick up electronic and magnetic fields over different frequencies. It's a theory that when ghosts are present they disrupt the electromagnetic fields.

This EMF detector will detect these disruptions.
Hand-held, lightweight and durable, with two easy to read scales (0-1 mG, & 0-10 mG), and dramatic audio signal. The favourite meter for demonstrating the presence of EMFs fields.

Digital Infrared Thermometer

This pistol-grip meter (with laser pointer for pinpoint accuracy) will measure temperatures from 0º all the way up to 600ºF at a safe distance. Offers an amazing 2% accuracy and a resolution of 1ºF. Field of view is 6:1, emissivity fixed at 0.95. Backlit LCD readout is easy to see, even in dim lighting.

Ghost Hunter's can use this device to detect and pin-point both "cold spots" and "hot spots" common with ghosts and paranormal activity. The next time you feel a cold chill run over your body you will know exactly how cold it was and which direction it went.
 

Infrared Beam Barrier

These are placed in for example doorways where nobody is allowed to enter in a controlled environment, if the alarm is triggered by crossing the beam, human interference can be ruled out.

Creates an invisible alarm barrier in seconds
20m (75ft) range

The receiver will sound whenever the invisible infra-red beam is broken. It can be set to chime once or chime continuously (with volume adjustable to low, medium or high) or set to a continuous high level siren. Each pair features a coded infrared transmission and a switch for high or low power output.