I like the idea of a sterilizing force-field. (Not like, sterilizing, but... sterilizing...) I enjoy speculation like that, but I am comfortable making the fo

I like the idea of a sterilizing force-field. (Not like, sterilizing, but... sterilizing...) I enjoy speculation like that, but I am comfortable making the following generalization: Corporations worth billions do not run physics experiments in densely populated areas, targeted at public land meant for public use. Disregarding that common sense, some other wild assumptions: Use static electricity as a subconscious cue to pay attention to a billboard nearby. Pavlovian training, too--associate your brand with a tingly feeling? Super-high-power RFID/NFC reading! Make a positioning system with increased accuracy using strong magnetic fields Gauge perceptive abilities by demographic groups, and willingness to experiment with curious physical sensations.