About 95% joking, but in that case, have everyone lock their phones in a tiny locker shelf thing and wand everyone with a nonlinear junction detector. If we get to the point in technology and battery capability where camera glasses are compact enough to be indistinguishable from ordinary metal eyeglass frames, we'll probably also have really good low cost portable tech to detect any on-body electronics (vs the flesh and clothing and metal accessories like belt buckles on a human body).