Any piece of equipment intended to capture evidence of the paranormal is only as good as the user's understanding of how that equipment works and its limitations.
Here are my thoughts about some of the "ghost-hunting" equipment that is commonly used.
Digital audio recorders (to capture EVP or "electronic voice phenomena")
Aside from the obvious attempt to capture the elusive EVP, I like having an audio record of the whole experience, not just an "EVP session". (Explained in more detail under "Methods")
Analog audio recorders
We've used this occasionally but found no real difference from results with the more-convenient digital versions.
Digital still and video cameras
I use these mainly to get photos and video of locations for reference and as a visual record of the locations. Audio captured by the video camera is also used for comparison with that recorded on the audio recorders.
By learning some technical aspects of photography, one will find that most visual "anomalies" can be explained.
Night Vision still and video cameras
They're just that. Another way to record information that can be analyzed for anomalies.
EMF meters, K2 meters
These seem to be one of the most misused pieces of equipment out there. You can't just ask questions and wait for a light to come on. Well you can, but so many things can affect the EMF meters that are NOT paranormal. These are good for debunking and finding electrical causes for some of the claims (like strange feelings, appliance interference, stuff like that).
EMF monitoring is good for backing up other possible evidence that may occur simultaneously.
But contrary to what one might see on tv, an "energy spike" of .1 or .2 is not an indicator anything paranormal going on.
Ours is the basic one. It has EMF meter and also reads temperature. Good to watch for changes occurring, especially if some other anomaly is caught at the same time. It also has a red flashlight that aids in the dark when you don't want bright light showing on video.
Contrary to frequent misuse that is seen on television, infrared thermometers don't measure "cold spots" in the air. They measure the temperature of objects.
Quite controversial. It states that it is for entertainment only, although many paranormal enthusiasts claim to have gotten very relevant words from it. It has both dictionary mode and phonetic mode. I think that phonetic mode would be less likely to be saying random words. If nothing else, it's fun to experiment. One can totally reprogram it with whatever words they choose. The voice and speed of spoken words can be changed and pronunciations edited by altering the phonemes. This can be learned by reading the instructions, a step most people skip.
ITC (ghost box) devices
I'll include the Shack Hack here since that's what we tried. It scans radio frequencies, giving little snippets of whatever is on the station as it scans over it. Lots of little one-syllable words that one might insist is a spirit and not a tiny part of a radio announcers speech. After experimentation, we don't use this because the sweep rate is too slow to avoid getting words and
phrases from the radio broadcasts.
We plan to experiment with the PSB-7. This device is quite different from the Shack Hack, having a much
faster sweep rate which can be adjusted. I would only be looking for phrases spanning over multiple sweeps, and not one-syllable words.
The beloved flashlight trick. Set the flashlight down, with the switch almost on but not quite, and start asking questions and telling spirits to turn it on and off. There is a very technical explanation out there about how this works, something about a heating and cooling cycle causing the light to go on and off. But on tv, it's a ghost!
Dowsing rods, Ouija boards, pendulums and similar
We don't use these for investigation.
In conclusion, I strongly believe that the single most important piece of equipment (aside from our brain) to use is a good quality audio recorder. I love my Tascam DR-05.