I used QR codes in the classroom to get students into random pairs last week. Each student was given a label with a QR code on. They had to scan themselves to see if they was an answer or a question. If they had a question they had to scan the other people in the class to find their answer.
For example if a student as 2+2 when they scan themselves they have to scan the other students in the room to see who has the number 4.