You can use pretty much any webcam or phone cam to see well into the infra-red. If you turn off the lights and look at the device - and especially at your hand

You can use pretty much any webcam or phone cam to see well into the infra-red. If you turn off the lights and look at the device - and especially at your hand using it - through such a camera, you are likely to see the IR and gain some extra insight as to how it works.