Is it possible that a person don't even know that they are actually a demon in human body?
I played with a pendulum, the pendulum never been wrong before (in my experience) and got curious and asked it what am I.. Then when I say am I human, it swings left and right (means no). Then I asked a few more (eg am I a vampire) it still swings left and right. Lastly I asked am I a demon, it swings back and forth slowly (means yes). I still continue asking am I a demon it still says yes. I even asked someone else to hold my pendulum and asked the same question, it still answers yes But I personally think that wtf? Furthermore, I felt interested with the topics about demons these few days.
I am a Christian, so you may not like my answer. When it comes to things like pendulums and Ouija boards I believe the answers come from demons themselves. I would suggest you leave the pendulum alone, get rid of it and call a priest or pastor to perform a house blessing (I do not believe an Exorcism is needed at this time but a house blessing may reveal the need.)