Next thing, hotels will use "microlens wallpaper", so the device becomes practically useless. See also: https://en.wikipedia.org/wiki/Nonlinear_junction_detect

Next thing, hotels will use "microlens wallpaper", so the device becomes practically useless. See also: https://en.wikipedia.org/wiki/Nonlinear_junction_detector#Countermeasures https://en.wikipedia.org/wiki/Nonlinear_junction_detector#Co...