In the film Never Let Me Go, the camerawork made the scanning of the armbands that the donors wore quite obvious at several points (at school, at the cottages, and even at Kathy's apartment.
What was the point of these? What it anything more than recording when donors came and went? If a donor ran away, it doesn't seem like having a record would really help with anything, since they have to actively scan them.
Does the novel expand on these devices more?