An ex-Paranormal Investigator turned Christian wrote an excellent post in regard to Familiar Spirits:
What is a familiar spirit?
Familiar spirits are demonic spirits, that respond to those that attempt to communicate with the dead, spirit guides, angels, aliens, or false gods. They mimick those that the sorcerer/necromancer/medium tries to “call up”. These spirits are closely linked to an individual, by either a person, place, or thing.
The most “common” way known, that a familiar spirit communicates with people, is through mediums.
What is a medium? The word medium — from the Latin adjective medius, “middle” — has several meanings that all center on the idea of being in between. 1.Medium means something that lies between two other points, people, or levels. 2. A person who transmits messages from the dead. (Familiar spirits)
Familiar spirits are not who they claim to be
These spirits are demonic spirits, that masquerade as our dead loved ones, spirit guides, aliens, angels, or false gods. They manifest in the form of whatever type of spirit that the person is seeking to communicate with. The most common type of spirit that people usually attempt communication with, is the spirit of a deceased loved one.
The reason for this is our natural emotions of grief and despair that we feel when we lose someone close to us, that we love. The enemy takes advantage of our grief. He does not play fair, and he is more cruel than many give him credit to be.
*The bible tells us that Satan transforms himself as an angel of light..
Demonic spirits have been here for thousands of years,
They have been around us and our families, all of our lives, for generations, knowing everything we do, or say, at all times.
When a person tries to communicate with the spirit of a “departed loved one”, via medium, EVP analysis, ouija boards, downing rods, pendulums, etc., the Familiar spirit will then respond, giving answers that are very personal, and only known by the “spirit” they are attempting to contact.
This “tactic” of the enemy, is the # 1 reason we have so many people in society that believie in “earthbound spirits of our departed loved ones”. These spirits are so convincing, that in most cases, it is impossible to deny that there is indeed “some kind of spirits” out there, that is attempting contact with us, that have personal knowledge of us and our dead loved ones.
These spirits are not only known to mimick the departed spirits of people we “knew personally”, but they also mimick the departed spirits of people that are “familiar to us” by a particular place, such as where we live. An example of this would be, if a person were to move into a new residence, and a familiar spirit makes its presence known, masquarading as a departed spirit of a person that once lived in that home, and died there. The familiarity in this case would be the residence itself.
It could also be places such as ancient Indian burial grounds, old war fields, or other places where people were killed or died.
Old Indian burial ground
Waverly Hills Sanatarium, which many people believe is one of the most “haunted places” on earth. While the building is now primarily a tourist attraction for those fascinated by the paranormal, it used to be a functioning tuberculosis hospital. In 1910, when the hospital was established, this meant a place where between 8,000 and 63,000 people died bloody, excruciating deaths, as there would be no real cure for tuberculosis until streptomycin was invented in 1943. Waverly Hills was also the site of at least two suicides, which strangely enough took place in the same room. With all of that suffering, it’s not surprising that rumors of ghostly apparitions, paranormal activity, and more have cropped up.
How these spirits usually work
Just as with any other sin, the enemy will try to “tempt us”. They will try to lure us into occult practices. Usually, soon after someone dies, a familiar spirit will attempt to make “contact” with us. They will try to make thier presence known. These attempts can range from the sound of footsteps, or things being moved on it’s own, disembodied voices, physical manifestations that can be seen, such as the form of dark shadow figures, orbs, or full bodied apparitions. It could also be strong smells of things that you would associate with a particular person, such as cigarette/cigar smoke, or perfume. It can also have bad smells, that smell like sulfur, rotten eggs, etc. The problem comes in when people do not “test the spirits”. Is this concept in line with scripture? When these spirits attempt to contact us, or make thier presence known, we need to rebuke it in Jesus name! When this is done, these spirits always flee!
If you or someone you know, is suffering from a haunting
After the spirit flees, as described above, if it returns, you must evaluate the situation. Usually, when there is any type of “haunting”, the familiar spirit has some kind of “legal right” to be there. Something must be contributing to an open door to the demonic. Are you, or someone in your household/family involved with any occult practices?
What are occult practices?
Deuteronomy 18 contains the most powerful biblical passage, outlining the occult. In verses 10 and 11, we find practices of the occult:
Deuteronomy 18:10-11 When thou art come into the land which the LORD thy God giveth thee, thou shalt not learn to do after the abominations of those nations. There shall not be found among you any one that maketh his son or his daughter to pass through the fire, or that useth divination, or an observer of times, or an enchanter, or a witch, Or a charmer, or a consulter with familiar spirits, or a wizard, or a necromancer. For all that do these things are an abomination unto the LORD: and because of these abominations the LORD thy God doth drive them out from before thee. Thou shalt be perfect with the LORD thy God. For these nations, which thou shalt possess, hearkened unto observers of times, and unto diviners: but as for thee, the LORD thy God hath not suffered thee so to do.
These demonic spirits are subject only to Jesus Christ.
These demonic spirits always flee at the name of Jesus! This is how we know that these familiar spirits are indeed demonic spirits.
Mark 16:16-18 KJV
 He that believeth and is baptized shall be saved; but he that believeth not shall be damned.  And these signs shall follow them that believe; In my name shall they cast out devils; they shall speak with new tongues;  They shall take up serpents; and if they drink any deadly thing, it shall not hurt them; they shall lay hands on the sick, and they shall recover.
You also may want to check out Spirit Guides Are Demons in Disguised.
If you don’t know Jesus Christ as your Lord and Savior, you can receive Him into your heart, and He can deliver you from darkness and sin and have your name written in His Book of Life.
If you are sincere, you can say this simple prayer to the Father (it doesn’t have to be word for word):
“God, I recognize that I have not lived my life for You up until now. I have been living for myself and that is wrong. Please forgive me of all of my sins just as I forgive others. I need You in my life; I want You in my life. I acknowledge the completed work of Your only begotten Son Jesus Christ in giving His life for me on the cross, I believe in my heart Jesus is Lord and was raised from the dead and I long to receive the forgiveness you have made freely available to me through this sacrifice. Come into my life now, Lord. Take up residence in my heart and be my king, my Lord, and my Savior. From this day forward, I will no longer be controlled by sin, or the desire to please myself, but I will follow You all the days of my life. Those days are in Your hands. I ask this in the Lord and GOD Jesus’ precious and holy name. Amen.”