As I was walking through the hallways of my dorm yesterday, I realized how the light shining through the peephole looked almost exactly a white HAL 9000 light. So, I decided to make a small LED light that would fit inside the peephole, and make it look like one of HAL's "eyes".

Step 1: Requirements

Since I live in a dorm, there were multiple constraints that I had to work within.

Restrictions:

The design must not limit the functionality of the peephole. Thus, the device must be either transparent, or easily removable.
It must not modify the peephole in any way.
The design must be low powered, I don't want to have 50 watts of power pumping into my dorm room.
And of course, since I am a poor college student, it must be low-cost.

Step 2: Parts

This project is very simple, and only requires 6 parts.

Wall wart: I used a 3.3 volt wall wart to power the entire device.
Wire: Some small gauge wire, preferably stranded for flexibility and durability.
Resistor: A proper dropping resistor for the LED.
Red LED: The most important part of the device, it needs to match the color of HAL's light. I managed to find an LED that matched the color of HAL's eye very well.
Rubber Stopper: This holds the LED in place inside the peephole.
Heat Shrink: I always use small gauge heat shrink to insulate the bare wires. You could always use electrical tape instead.

Step 3: Prepare the Rubber Stopper

I used a rubber stopper cutter to cut a hole big enough to fit the cable in. It took several bores, with me ending up using a massive cutter because the stopper was ancient and hard as a rock.

Step 4: Solder Everything Together

Place heatshrink on the wires before moving on. It is always embarrassing when you have to start over because you forgot the heatshrink... not that I know by experience or anything...

Pull the rubber stopper down away from the work end. Solder the resistor directly to one of the legs of the LED.

Then, solder your cable to the LED and resistor.

On the other end of the cable, solder the wall wart cable to the power cable.

If the wall-wart you are using has a long enough cord, you don't need the cable. I needed the cable because I need to reach about 8 feet to the nearest plug...

Make sure everything is the correct polarity using a multimeter.

Step 5: Wrap It All Up

Shrink the tubing, and if necessary, use electrical tape. Ensure there are no bare wires up by the LED and resistor, because it is going to be a tight squeeze up in the stopper, and you don't want to have to debug a short up there.

Once that is all done, push the stopper up to the base of the LED, so that it covers the resistor.

Step 6: Place in the Peephole

Put the stopper into the peephole, and plug in the wall wart. I used small 3M Command hooks to secure the wire to the door. Eventually the blue painter's tape in the image will be replaced with Command Hooks. Make sure to leave enough slack between the door frame and the door so the cable doesn't get ripped off of the wall, and between the stopper and the first hook, so you can remove HAL to look inside.

Make sure to unplug HAL if it starts to think on its own.

Also, I take no responsibility if HAL begins to disable life support in your room, or if it locks you out, and you have to brave the vacuum of the great outdoors to get inside