Someone gave me a necklace with some symbols, numbers and shapes. He claimed that it would protect me from Satan. How do I know if it is a spell or not? If it is a spell, how can I undo it?

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

In practicing their evil deeds, sorcerers and astrologers use symbols, numbers and figures. They claim that these figures are based on astronomy and can be used to tell about earthly incidents.

According to Shaykh al-Islam, Ibn Taymiyyah there is no doubt that what they do is magic and sorcery and these are both prohibited by the Sharee'ah. It is also prohibited by the Sharee'ah to wear such objects or to seek the help of sorcerers.

It was narrated on the authority of Ibn ‘Abbaas that the Prophet, sallallaahu ‘alayhi wa sallam, said that to learn astrology is to learn a subset of magic. [Ahmad, Abu Daawood and Ibn Maajah: Saheeh] This Hadeeth indicates that astrology is a subcategory of magic. Allaah The Almighty Says (what means): {And the magician will not succeed wherever he is."}[Quran 20: 69] Observation has proved that astrologers do not succeed in this life; and they will not succeed in the Hereafter.

Symbols and shapes are usually used by magicians and not astrologers. Every shape, number and figure has a Satanic significance. Therefore, do not wear or use the necklace. 

To undo the spell, you can recite over it the Quranic verses which annul magic, such as the verse of Al-Kursi [Quran 2: 255], the chapters of Al-Falaq and An-Naas. Do this while exhaling some moist breath. Then, you have to remove these figures from the necklace with a file, bury the necklace in a place and cover it over with earth, or you may scatter them in the sea, river or running water. 

However, to avoid any harmful mistake when undoing the spell, you may seek the help of a righteous Muslim who is well- acquainted with such matters and have him undo it for you.    

And Allaah Knows best.