Demon
The contemporary Roman Catholic Church unequivocally teaches that angels and demons are real beings rather than just symbolic devices. The Catholic Church has a cadre of officially sanctioned exorcists which perform many exorcisms each year. The exorcists of the Catholic Church teach that demons attack humans continually but that afflicted persons can be effectively healed and protected either by the formal rite of exorcism, authorized to be performed only by bishops and those they designate, or by prayers of deliverance, which any Christian can offer for themselves or others.
Exorcism in Christianity
The traditional method for determining if a person needs a deliverance is done by having someone present who has the gift of discerning of spirits. This is a gift of the Holy Spirit from 1 Corinthians 12 that allows a person to "sense" in some way an evil presence. While the initial diagnosis is usually uncontested by the congregation, when many people are endowed with this gift in a single congregation, results may vary.