In Phasmophobia only EMF Level 5 counts as evidence to identify the type of ghost in your Journal. Lower levels may count towards objectives on the white board in the truck but these do not count for the journal. Watch your EMF Reader carefully as you may only get EMF Level 5 once or twice depending on the ghost and its location. However, even if it only shows once it is still one of the three pieces of evidence that you need in your journal. Keep in mind that not all ghost types will produce EMF Level 5.
Keep in mind that leaving the EMF Reader on when you no longer need it can drain sanity, produce a lot of noise, and distract the ghost from other interactions such as writing in the book.
Also remember to check the White Board in the truck to see if the ghost will respond to everyone, or only a person that is alone. If the ghost only responds to people alone then one person will have to be alone in the room, or possibly alone in the house.
Once you have started collecting evidence you can use our Ghost Identifier to help you quickly determine what kind of evidence you should be looking for and what evidence you won't find.