Hidden Compartment in a Coin (with Stuff You Already Have!)




About: I am a teenager, building since I was 4 (and soldering since I was 7). I enjoy building things and inventing all kinds of little projects, some of which I share here!
One of the classic spy tools is the hollow coin where our hero (Or nemesis!) hides some microfilm, micro SD card, or a secret message. In real life, this was also used by the Soviets, when they were discovered because they were accidentally spent and dropped to reveal a hidden compartment! (Thankfully, my design does not have this flaw.)
Now, it is easy to see how cool these things are, and I decided to do some internet research. However, they seem to go for about 20.00 US dollars. I think that’s a ridiculous price to pay, especially when we can make our own with some time and money. As a result, I decided to make my own!
You can read on, or you can see the video version (The written version is more descriptive, but if you want the abridged version, check it out)

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Step 1: Supplies

Seeing as this is a fake coin I was making, I choose to use the biggest commonly available US coin there is: A quarter. A nickel could also work, but then the compartment would be smaller.
So, in addition to 3 quarters, you will need…
Some info to put in it (A slip of paper, or microfilm, or even a small enough memory chip)
For tools, you will need…
-Dremel motor tool
- Drill and drill bits
- Files
- Clamps and vice (To keep our coins from getting away!)
-Solder and Soldering iron
- Hot glue/ Hot Glue gun
-Gloves (For safety!)
And a whole lot of patience. You will see why later, but believe me; it takes a lot of tries to get one of those faces just right.

Step 2: Getting the Face

We want our coin to be hollow. This means that we won’t need most of the coin, and so in order to make 1, we will be removing the majority of 3 coins and putting them back together like a secret agent version of Frankenstein.
To get only the face from each side, I Dremeled  down through the first face, and kept on going through the copper sheet. I stopped when I hit the face  on the other side- I didn’t want to go all the way through! I did this to 2 coins so that I had both the front and back face of a quarter.

Step 3: Getting the Body

Well, this is looking good and all, but I still didn’t have the main body. To solve this problem, I took a quarter and using sequentially larger drill bits, created a hole in the center. I widened and cleaned the rest up with the Dremel.

Step 4: And It All Comes Together!

So, to put it all together, I soldered one side to the ring and hot glued the other. I made sure I only used a little bit of hot glue in one spot, as the goal here isn't to keep the face on, but to allow it to act as a hinge/spring. By keeping it small, the hot glue will bend and allow the coin to open slightly, clam shell style. It will then go back into place when released. I cleaned up the solder with a file, and I was good to go!

Step 5: TaDa!

When it is all together, you can hide small bits of info, from a slip of paper, to microflim, or even a micro SD card. The one I have is 4 gigabytes, and that can store about 4294967296 characters. (According to the internet.) Close inspection proves it has been tampered with when it is on its own, but put it with some others or keep people from focusing on it and they will never know! (This isn't hard to do- How many people carry around only 1 quarter, and who stares at the quarter some other guy has in his wallet?) Please let me know your questions and ideas on this Instructable! Good luck in making your own, and as always, Have a nice day!

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    136 Discussions


    5 years ago

    this is awesome! I can imagine exchanging secret messages with my best friend with this

    1 reply

    Reply 5 years ago on Step 5

    It depends on your intent. The statute reads:

    Whoever fraudulently alters, defaces, mutilates, impairs, diminishes, falsifies, scales, or lightens any of the coins coined at the mints of the United States, or any foreign coins which are by law made current or are in actual use or circulation as money within the United States; or Whoever fraudulently possesses, passes, utters, publishes, or sells, or attempts to pass, utter, publish, or sell, or brings into the United States, any such coin, knowing the same to be altered, defaced, mutilated, impaired, diminished, falsified, scaled, or lightened - Shall be fined under this title or imprisoned not more than five years, or both. [Emphasis added.]

    This is why penny pressing machines are legal.


    They are currently trying to pass a law that makes it illeagle to melt down penny to collect the copper... the penny has more copper value in it than it does monitary worth.. Even the new(ish) penny's that are only plated with copper are worth more than the face value...


    Reply 1 year ago

    "Illeagle", my UK based friends, is something unlawful in the USA ;)


    Reply 3 years ago

    Penny machines should be illegal LOL.. they charge $1.00 .. it's highway robbery lol


    Reply 3 years ago

    The law merely states that coins cannot be manipulated to your own advantage

    Yes, but only if I use it for illegal things (Counterfitting, etc.) Also, the Secret Service has more important things to worry about than some kid messing with quarters.


    Reply 5 years ago on Step 5

    Not true. I just finished watching a program on the National Geographic's Channel on the US Mint. The director of the mint was asked about what a person can do to money they have. He stated: "You can do whatever you want to with a coin or bill. It's your money, you own it." He further commented that as long as you didn't attempt to defraud someone like perhaps attempting to turn a $5 bill into a $50 bill, anything you want to do is legal.


    Reply 4 years ago on Introduction

    The law as of December 2006 specifically prohibits the melting of pennies or nickels FOR THEIR METAL VALUE. Exceptions include jewelry and works of art. Check when the National Geographic's Channel production date.


    Are you aware that it's illegal to sing happy birthday in public without paying royalties to Warner Chappell?