Spanreed

By splitting an infused ruby and embedding the halves in pens, a certain kind of Pairing Fabrial called a spanreed is created. One spanreed mimics the action of the other spanreed, even across a great distance. To signal the start of a conversation, one person twists the gem on their spanreed to cause it to blink on the other person's spanreed. The first person writes their message, causing the other spanreed to do the same, and then turns the gem when they are done to indicate that it is the other person's turn to write. Shallan and her brother Nan Balat and Dalinar and Jasnah are shown using spanreeds to communicate with each other.