The EMF detector is one of the gadget that you will use to detect the presence of a ghost in the area. Use it on the Prison Island.
How to Get the EMF detector
Head out of the house and then run over to Main Street. Go inside the bakery and talk to Jane the baker. Tell her, “Fiona sent me.” She then walks over to the pastry case and it sinks into the ground. A new case rises up to replace it and it contains all kinds of cool ghost hunting gear! One of which is the EMF detector.