Introduction: Invisible Signally Beacon (Infrared LED Throwie)

Picture of Invisible Signally Beacon (Infrared LED Throwie)

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

Picture of 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.

Step 2: Materials

Picture of Materials

Here are the materials that you will need for this project:

Infrared LED
1.5V Button Cell Battery
Electrical Tape
Small Magnet  (optional)
Digital Camera

Wire Cutters

Step 3: Bend the Leads of the LED to Fit the Battery

Picture of Bend the Leads of the LED to Fit the Battery

The first thing that you need to do is bend the leads of the LED so that the button cell battery can fit between them. This works best if you leave the shorter lead straight and bend the longer lead to match the shape of the battery. 

Step 4: Insert the Battery Between the Leads of the LED

Picture of Insert the Battery Between the Leads of the LED

Insert the battery between the leads with the positive side touching the longer bent lead and the negative side touching the shorter straight lead. Use your fingers to squeeze the leads against the sides of the battery. Hold the LED in front of a digital camera to verify that it is working. It should appear as bright purple on the screen.

Step 5: Trim the Leads of the LED

Picture of Trim the Leads of the LED

Next you need to trim the leads of the LED so that they don't stick out past the battery. 

Step 6: Wrap the Battery in Electrical Tape

Picture of Wrap the Battery in Electrical Tape

To hold the battery and the leads in place, wrap them with electrical tape. 

Step 7: Stick a Magnet to the Side of the Beacon (optional)

Picture of Stick a Magnet to the Side of the Beacon (optional)

The simplest way to set up your beacon is to just set it on a flat surface. However, this gives you limited options to work with. Another option is to mount the signal beacon with a magnet. This will let you attach it to any metal object. Just take a strong magnet and stick it to the side of the battery. You can then stick it to any metal object that you come across. Not only does this give you more locations to work with but it also lets you point the LED in more directions.

Step 8: Use the Invisible Beacon to Signal Your Accomplices

Picture of Use the Invisible Beacon to Signal Your Accomplices

This beacon is small and difficult to see (especially at night). You can set it up just about anywhere without attracting attention. Your accomplices will be able to see it with any digital camera. Cell phone cameras are ideal for this. To anyone watching, it will just look like they are texting or surfing the internet. This is a fun tool to add to your spy kit.

Also, please remember to retrieve you beacon later so that it doesn't litter the ground.


AsdOmega made it! (author)2017-06-12

Great and easy Idea!! Exactly what I need for my Night - Treasure Hunt

Cyraxgreen (author)2017-06-05

hi, i got Led Ir color black and...

read this first for a idea


1. Emitted Colour : Infrared.

2. Size: 3mm.

3. Lens Color : Black Clear.

4. Forward Voltage (V) : 1.2-1.4V.

5. Wavelength (nm): 940nm.

the 1k resistor is good for the led with battery 3v?

What is the current rating of the LED?

I think 100

To find the resistor, subtract the supply voltage from the device voltage. Then divide by the device current rating in amps. So (3 - 1.5) / 0.1 = 15 ohms.

kevsaul (author)2014-03-10

The camera trick does not work on my iPhone 5s but does work on iPad 2

Tanmayg (author)kevsaul2015-04-19

It doesn't work with my iPod too. I don't know why.

There are a few cameras that have an infrared filter to try to block more of the near infrared spectrum.

Jan_Henrik (author)kevsaul2014-03-10

You I-Phone has an Infrared block filter, which blocks infrared Light! Most DSLR´S have them :)

Suraj Grewal (author)2014-06-27

Throw that in a battlefield and watch the laser guided missile hit

Gula (author)2014-05-28

Look at is with the camera on the screen side, it does not have a ir filter.

Ploopy (author)2014-05-27


About This Instructable




Bio: My name is Jason Poel Smith I am a Community Manager here at Instructables. In my free time, I am an Inventor, Maker, Hacker, Tinker ... More »
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