In theory, the same should be possible with IR light instead of the visible one. Many (all?) digital cameras are infrared-sensitive, which is easy to test by ju

In theory, the same should be possible with IR light instead of the visible one. Many (all?) digital cameras are infrared-sensitive, which is easy to test by just pointing a TV remote at a camera and pressing a button. So one can simply do a morse-ish code in IR and then have an app parse it out.