According to experts in the field, spirits can only take form or perform an action when they have enough energy to do so. Since ghosts don’t eat (that we know of), the only way for them to get energy is to take it from the surrounding environment. This energy can be heat from the air, heat from our own bodies, electricity stored in batteries, etc.
Sometimes it’s only a small area within a room that feels colder. This is referred to as a cold spot. Other times it may be the entire room that gets cooler. In order to verify an actual temperature deviation, paranormal investigators use digital thermometers, thermal cameras, and other devices to measure ambient temperature throughout the room and surrounding objects.
If a cold spot or reduction in temperature has occurred, it’s usually a good time to try and capture a voice recording (EVP).