Extech RH350 Superheat Psychrometer
The are three main devices for measuring temperature on an investigation: standard thermometers, psychrometers, and IR thermometers. It's important to be able the get a reading of temperature differences, because it is theorized, and evidence so far seems to support, that paranormal activity draws upon ambient energy to manifest, including surrounding heat energy. So the classic "cold spots" common to many places with paranormal activity are most likely an example of the heat energy being drained.
The first device is of course just a regular thermometer. It's best to get on with a digital readout. There are thermometers available that have a base unit and several remote sensing units. These are great because you can monitor the temperature at your location and three or more remote locations without moving about. The main drawback to regular household thermometers is that they usually register temperature changes slowly and that they're often not incredibly accurate.
The second device is a psychrometer, which is mainly what SEPRS uses for temperature measurement on investigations. This device is generally used for scientific and industrial temperature measurement, and is generally very accurate and quickly registers temperature changes. Most psychrometers come with two or more leads, and therefore they're great to walk around with to chase cold spots. The way you do this is to mount the psychrometer to a pole of some sort, run one lead to the end of the pole, and leave the other lead at the base of the pole. That way, if you walk into a cold spot, the lead on the end is going to give you a different reading than the lead at the base. Generally, temperature differences on the two leads of 5°F or more are significant. Most psychrometers also measure humidity, and save readings into memory. The model we use is the Superheat Psychrometer and run about $130.
Extech RH350 Superheat Psychrometer
Another popular device among paranormal investigators is the IR thermometer. These shoot an IR beam and give you a fairly accurate reading of the temperature of whatever the beam is hitting. The drawback to these is that they only measure surface temperature, where with paranormal investigation it is important to be able to measure the air temperature. We have several of these thermometers, but because of this drawback, we don't use them extensively on investigations.