Thermometer
Thermometer or Thermal Scanner - Thermometers are an instrument that is also very useful There are two types used regular digital thermometers and infrared non contact thermometers. When used on an investigation this will aid as a detection system for spirit presence. Rapid temperature drop of 10 degrees of more could indicate spirit presence. I recommend using the infrared non contact thermometers but cause they react in less than a second to a temperature drop and you can scan a large area quickly.