Wamba the Fool said:
It says in James
There's a diffence between believing and being saved. So, of course they believe in God, but they rebelled against Him and wanted power for themselves. That's why they got kicked out of Heaven in the first place.
The demons, which are those 'unclean, foul, spirits', were never in heaven in the first place.
Their father's were, according to Scripture; but they are born of the rebel angels of daughters of Adam and are condemned from the conception of them as unclean spirits. When they are disembodied by the death of their unclean flesh, they roam the earth, seeking to inhabit a body, doing evil, unless they are sent to the pit before their appointed time for worse deeds than just 'unlawfully' existing.
The Scriptures that we have provide abundant proof that, on this matter, that the book of Enoch is correct and rightly quoted in Scripture.
So, no; the demons believe that Jesus Christ is the Holy One (as they confess in the Word) who was to come, and are never saved, as the angels who fell believe -even Satan- and are never saved.
Believe with the heart and confess with the mouth that you trust Him to be and do what He promised and you will be saved, because with that confession comes the humbling of yourself to His Word and agreement with Him of your need.
The fallen angels and the nephillim born of them never had a promise to be saved by the blood of sprinkling, which is only for the 'Adam- kind' -'from the foundation of the world'.
It is not to angels that He gave aid, when He took upon Himself the garments of vengence (the human nature), by clothing Himself with the body prepared in the Womb of the virgin, in which body He is the Kinsman-Redeemer/Avenger of all in Adam (whosoever will).