Melly,
Congrats on the new EMF detector! New "Toys" are always fun, no matter what they are.
So, as Wes mentioned, EMF detectors in themselves are not really reliable to determine the presence of spirits. The best use of them is to attempt an interactive session. In other words, find the standard value for an area and then ask a spirit to move in front of the meter or move around it. If the meter registers then you have something to start with.
Once that happens, then try to prove that it is actually interactive and will respond to your queue. Also try not to move your hand or anyone else's body near it when you're doing this. That could invalidate the results.
Many things can trigger EMF detectors such as cell phones, walkie talkies, motors, metal objects being moved rapidly, or even just the presence of a metal object such as a picture frame or spoon can act as an antenna to pick up radio waves.
I look forward to hearing your results. But above all, don't get scared or worried. Spirits are likely around you at various times and you just never know it. In most instances its nothing to worry about. Treat them with respect, and treat the tools of the trade with respect and dignity and not as a game. That tends to go a long way in this field. And don't provoke, people don't like it when they're alive and they like it a whole lot less when they're passed. And pissing a spirit off is probably not the best way to get the ball rolling so to speak.