Here is an instructable for some espionage. Muhahaha.
The spy light is an infrared LED light contained in a bottle. Invisible to the neked eye Infrared light can be viewed on most modern cell phones, you just need to know how to hack it.
I made my first one of these out of boredom, and a spare Infrared LED I had laying around. The original one was soldered to the wires, in keeping with the espionage theme I've opted for the "field/dirty" version using electrical tape.
I shall now proceed with Project Spy Light, code name: spaghetti bottle.

Step 1: Materials

For this project you will need:

- electrical tape
- solid core wire
- 1 battery
- empty bottle( doesn't matter what kind)
- Infrared LED
- alligator clips with wires attached

Step 2: Step 1

With the solid core wire strip both ends.
Choose one end and begin twisting it around one end of the LED contact.
Do this for both sides with the two separate wires.
Now take the electrical tape and wrap around the wire and LED contact.

Step 3: Step 2

Now making sure the bare wires are not touching each other, begin twisting the two wires around each other as pictured. Remember to leave some space for later.

Step 4: Step 3

Now you will need to take the bottle cap and begin carving out you're hole. A sharp knife in twisting motions will do the job. Make the hole big enough for the two wires to fit into snugly.
Now feed the wires through and secure them with tape, if you prefer.
For any interest the handy little knife is a senrenmu, a chinese brand and great little tool.

Step 5: Step 4

now you can twist on the cap and prepare the battery.
If you want to you can rig up the wires directly to the battery. I chose to use some alligator clips with wires already on them. I taped the wires to the positive and negative points on a battery. That's just my quick method. If you wanted to have a more permanent version you could rig it up to a USB cable. Although with that method you would need to prepare for the voltage with a transistor. Fare warning.

Step 6: Hook Er Up

Now you can put the battery to the wires and watch it glow!
Well, not quite yet, you will need a cell phone to be able to see it. Luckily I hacked my webcam and took out the UV filter, which does pretty much the same trick.
The first pic is of the bottle taken with my camera. The second is the bottle taken with my webcam with the filter removed.
As you can see the light is very bright.

I hope you enjoyed this ible' and will find a few uses for this little project. One that strikes me is a nifty "Invisible" light for mores code.