Thermometers are often used to detect cold or warm spots at a location to either demonstrate that a ghost is present. A thermometer may detect a temperature drop of 5oC, but all that the thermometer tells us is that the temperature has dropped and not why or how.
To some that reading would simply mean the temperature has changed in the room through natural causes, but to others it might indicate the presence of a ghost. Of course, the thermometer hasn’t told them this, it’s simply their interpretation of the reading – influenced by their expectations, just like the glass used for glass divination.
Ghost hunters sometimes use laser thermometers without realising that the device is measuring the surface they are pointing it at, and that the output of such a device can be influenced by the hand that is holding it moving it around too much. Not to mention the mundane causes such as central heating, draughts and more that could cause a surface to cool down or heat up.
Some ghost hunters will use thermal imaging equipment in an attempt to see a visual representation of cold or warm spots, and even apparitions. However many anomalies captured on Thermal Imaging equipment are caused by visual illusions. Cold and warm spots detected often have similar causes to those detected by thermometers.
The picture below, for example, was captured by ghost hunters who claim it shows a ghostly apparition. The actual cause is a reflection on a metallic surface. The use of this equipment is misleading – especially when the users do not understand how to use it.