On our investigations we use many things to guide us our conclusions whether a place is believed to be haunted or not.
EVP: (Electronic Voice Phenomenon) hand held digital recorder that when we walk through the property we ask questions and pause for a few seconds as to wait for an answer. The theory to this is that we hope to retrieve answers to our questions from the Ghost or spirit. Later when you are reviewing the recordings you may hear either direct answers to our questions or normally some kind of sound or noise that was not heard by the investigators at the time of the recording.
EMF: (Electro-magnetic Field) there are electromagnetic fields all around you at all times. How this tool helps you during investigations is simple when something is trying to manifest its self it has to draw energy so when this is happening the Electromagnetic Field around you will rise the higher it goes the more visible or vocal it can become. So when the EMF detector is reading a higher range in that area you can take pictures or use EVP to ask more questions. It is kinda like a tool used to pinpoint a Ghost.
Digital Thermometer: this is also used to locate spirits or a vortex much like the EMF only it does it with temperature. You will most likely be able to actually feel the cold spot personally the actual thermometer will just tell you the exact temperature of the area you are feeling. It is usually a dramatic change in temperature at least over a 10 degree drop.
Video Camera: It is always a good idea to have at least one video camera running in an area at all times so you can catch anything happening when you are not there or if you are in the room you have video evidence of what is happening.