The state-of-the-art tool for finding cold spots in the air is a temperature-measuring device called the "digital
thermometer/pyrometer" (DTP). It is a thermo-coupler thermometer that is more advanced and specialized than
a standard digital thermometer.
The DTPs manufactured by TIF Instruments (www.tif.com) scan the temperature of the air 3 times per second. They range in price from $129 to $199, depending on where you buy them.
Unlike the IR thermometers, this measures actual air temperature. It does not the temperature of surfaces, although it can do that with one of its attachments. This allows you to locate cold spots in the air as you walk through a room.
It is expensive compared to other thermometers, but itís the one thermometer that actually does what a paranormal investigator requires. Namely, it gives immediate, "real time," temperature readings of the air around the investigator.
Standard IR thermometers are also "real time," but they measure the temperature of the surface of whatever object at which they are pointed. When pointed across a room, the IR thermometer gives the temperature of the wall on the other side of the room, not the temperature of the air in-between.
Other digital thermometers have temperature probes that are large relative to the DTP from TIF Instruments. It can take several seconds or more for them to take an accurate reading. By that time, you are already past the cold spot in the air or the probe is through the cold spot before it even has a chance to register it. This is because digital thermometers measure the electrical resistance within the probe. They register temperature based on the temperature of the probe itself, not the air around it. The temperature of the air must change the temperature of the probe in order to register.
The DTP by TIF Instruments uses a wire that is smaller than a human hair for its probes. These wires react very quickly to the temperature of the air and give almost instantaneous readings of air temperature. According to TIF Instruments, its DTP thermo-coupler takes the "real-time" temperature of the air around its probe 3 times per second.
Itís a bit pricey, but you want to invest in the right tool for the job.