Black tourmaline is an excellent stone to have in your home and to carry with you.  It's known to repel negativity and to protect you from it so keeping a small piece on you is a great idea especially when you're out in large crowds.   Black tourmaline is also said to deflect electromagnetic waves or frequencies (EMFs) that are emitted from most electronics. Exposure to EMFs are known to cause tiredness, stress, and sleep disturbances as well as many other symptoms.  To prevent the negative side effects of exposure to EMFs you can place this piece of black tourmaline near your computer or other electronics to absorb the EMFs.