We recently wired up some drawers of 3D glasses on charge so that when someone opens a drawer, ceiling lights come on.

Control was accomplished with a Crestron system controlling a Lutron panel, so the lights would only be activated if they were off, not if the house was at full lights.

The heart of this is of special note because it's so dead simple: If there's something closer than about 2" to it, the two output wires have no voltage on them. If there's something more than about 6" away, the output wires have the input voltage on them. Input voltage can be between 12 volts and 24 volts.
Here's what it looks like. The tube is about 1/2" in diameter:


The bracket can be removed for mounting these in a 9/16" hole. (Their data says 13 mm, which is too small, AND it says 14 mm somewhere else.)

They work between 2" and 6" because the actual switching distance depends on how reflective the target is. Black paper, it switched at 2." My hand, it switched at about 4." White paper or a mirror, it switched at about 6."

These are intended by Wessel LED, who imports them, to directly drive strings of LEDs, and they can output up to 30 watts. Their information is horribly non-technical, so I can't tell you if that's 30 watts at 12 volts but less at 24. Also, the devices have connectors on them that work with Wessel parts so the non-technical person can just string things together, but which Digikey could only come close to identifying. Wessel has no idea what the connectors are! (Maybe if a half dozen of you emailed them saying you want to use this product but you need the specs on matching connectors....)

There's only one caveat to using them: they don't switch the hot, they switch the ground. We put four of them together so opening any one drawer would turn on the lights. Since it's natural for us to connect all grounds together, I did that and found that it would not switch off. Input and output grounds cannot be connected to one another.

Anyway, this was a nice find. Enjoy.

Wessel LED is in Florida.