Spies need ways to secretly communicate with their partners. This can be a simple signal like a chalk mark on a wall or a newspaper left on a park bench. But the best kind of signal is completely invisible. In this project, I am going to show you how to make a simple invisible beacon that you can use to signal your friends and accomplices.
Step 1: How the Invisible Beacon Works
This design uses an infrared LED as the signally device. Infrared light is invisible to the human eye. However, digital cameras are able to detect these wavelengths. You can observe this by pointing your TV remote at a digital camera and pressing a button. To the camera, the infrared LED will appear to light up bright purple.
By using an infrared LED and a digital camera, you can send and detect signals that will be invisible to everyone else.