I know it exists for some Android devices, but can also an iPhone (4, 4S, 5, 6...) "see" and display infrared light that is captured by its camera?
So apparently only the front camera (the one facing you) allows it. (The back one filters infrared).
Point a tv remote control to the front lens with Camera app on and you'll see the little precious beam.
Found it here: http://www.instructables.com/id/See-Infrared-LED-Light-with-an-iPhone-4/