Question

how does the demonologiest find the paranormal presence according to the presence of emf at that place ??

Answer 1

Demonology is the study of demons or beliefs about demons,[1] especially the methods used to summon and control them. The original sense of "demon", from the time of Homeronward, was a benevolent being,[2] but in English the name now holds connotations of malevolence. (To keep the distinction, when referring to the word in its original Greek meaning English may use the spelling "Daemon" or "Daimon".)

Demons, when regarded as spirits, may belong to either of the classes of spirits recognized by primitive animism.[3] That is to say, they may be human, or non-human, separable souls, or discarnate spirits which have never inhabited a body. A sharp distinction is often drawn between these two classes, notably by the Melanesians, several African groups, and others. The Arab jinn, for example, are not reducible to modified human souls. At the same time these classes are frequently conceived as producing identical results, e.g. diseases.[4][2]
The ascription of malevolence to the world of spirits is by no means universal. In Central Africa, the Mpongwe believe in local spirits, just as do the Inuit; but they are regarded as inoffensive in the main. Passers-by must make some trifling offering as they near the spirits' place of abode; but it is only occasionally mischievous acts, such as the throwing down of a tree on a passer-by, are, in the view of the natives, perpetuated by the class of spirits known as Ombuiri.[11]

So too many of the spirits, especially concerned with the operations of nature, are conceived as neutral or even benevolent; the European peasant fears the corn-spirit only when he irritates him by trenching on his domain and taking his property by cutting the corn;[12] similarly, there is no reason why the more insignificant personages of the pantheon should be conceived as malevolent, and we find that the Petara of the Dyaks are far from indiscriminate and malignant, being viewed as invisible guardians of mankind

(it's is from willkipidea of demonology)