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

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

My Instructable was featured on LifeHacker! (I'm very proud...)

Step 1: Supplies

Picture of 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

Picture of 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

Picture of 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!

Picture of 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!

Picture of 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!


MajorWebUser (author)2013-12-15

Are you aware that it violates federal law to deface currency?

ActionAbe (author)MajorWebUser2013-12-15

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.

SlickSqueegie (author)ActionAbe2013-12-21

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...

deluges (author)SlickSqueegie2017-10-13

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

deluges (author)deluges2017-10-13

that or a sick bird.

ActionAbe (author)SlickSqueegie2013-12-21

But it's not illegal *yet*, and that's all that matters.

kasssa (author)ActionAbe2015-06-14

Illegal as of December 2006! Applies to pennies and nickels.

kasssa (author)SlickSqueegie2015-06-14

Illegal as of December 2006! Applies to pennies and nickels.

mrsnone (author)ActionAbe2016-04-12

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

MiguelM97 (author)MajorWebUser2016-05-10

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

joyewils (author)MajorWebUser2016-04-13

Is that all you can say? Who cares anyhow!!!!

KellyD3 (author)MajorWebUser2016-04-13

seriously, who cares.

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.

Here here!

veeguy (author)MajorWebUser2013-12-15

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.

kasssa (author)veeguy2015-06-14

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?

KevinG227 (author)2016-12-05

I was a paperboy in Jersey City delivering the Jersey Journal. I was given a hollow quarter as part of the payment for the paper. I noticed it when dropped onto the tile floor in the hallway of the apartment bldg. the quarter looked real. back then the quarters were either all or mostly silver, not the copper band ones. as soon as it hit the floor the sound was something weird. the coin was assembled like a chocolate coin in foil.

ggarcía-2 (author)2016-08-23

The very big problem is to pay with the "special coin", and all your files on the SD will go directly to the trash!! XD LOL

tpeterson1959 (author)2015-06-14

Nice job!

It's actually a myth that the coins were used to transport files, but there is a basis in reality for the myth behind it. U-2 pilots (and other covert operators) carried a coin with shell fish toxin embedded in the grooves.

I worked as a magician during college and used the "Scotch and Soda" trick as part of my routine (it's available on Ebay and Amazon, as well as a multitude of magician supply websites - none of which existed when I was using the routine!).

After college I worked for a government agency where the coins were demonstrated as being "bad" concealment devices in a class related to the job - but they had no idea why one of the coins was a Mexican Peso. I quickly demonstrated why. I also demonstrated what the ring was for - separating the face from the body.

What make using a hollowed out coin as a concealment device "bad" are weight and sound. In order to make a space large enough for even a micro dot, enough material has to be removed to give reason to look at the coin more closely if it falls into the wrong hands. If it is dropped, even casually, it sounds "off," also drawing attention.

You did an excellent job making the coin! Just make sure you don't accidentally spend it!

while it may not be the best way for a "spy" to transport, or hand off microfilm. Just recently on AHCs forgotten history they did a story on how a soviet agent was discovered because he tipped his paperboy with a hollowed out nickel that contained a file. The child discovered the coin wasn't "real" and threw it on the ground. When it hit it popped open, and out came a microfilm.

StuartT1 (author)tpeterson19592016-04-14

Most definitely NOT a myth.

A friend of mine found one in exactly the way mentioned. Dropped some coins when cashing up, and it separated when it hit the floor. It was a UK 2 shillings, which at almost 1.1/8" is quite large.

Some years after this, I saw exactly the same type of coin in the spy museum in Tampere, Finland.

Infinity57 (author)2015-06-17

For those with a milling machine, it is even easier and prettier.

Mill the first coin paying attention has depth.

For cover reduce the coin like any piece of metal and voila

Note that I have not tried it but if someone wants to try :)

theegghead (author)2014-01-18

I love secret compartments! This one is downright AWESOME!!!

hope you win the contest!

I'm so glad you enjoyed! (I hope I win too!)

KhoiS (author)assemblyrequired2015-06-15

You won! (I saw a golden medal on the top right corner of the page)

CeeK (author)2015-06-14

That is pretty cool in terms of spy stuff. Would make it so easy to pass information unnoticed.

Imagine how much information you could fit inside an Australian 50 cent coin! But I know it's definitely illegal in Australia to do that, since at least one person in the last 10 years has been charged for writing on money in permanent marker (even though since it's polymer money, you could probably clean it off).

So, I might save this one for some dystopian future where all my communications are monitored, but I can somehow still pass coins to people. And movies, with permission.

shawno1143 (author)2013-12-26

this is a felony

_xXJuanXx_ (author)shawno11432015-06-14

ppfft who cares? what isn't a felony these days anyway.

1) No, it isn't. The federal law makes it a felony only if it is being used for illegal acts or being passed off as a real coin.
2) Even if it was, it wouldn't matter: the federal law has bigger things to worry about than some kid drilling into 3 quarters.
3) It's my money, so as long as I treat it as it is (Not real money), then there is no problem.
4) Artists do this sort of thing all the time, as do tourist attractions (Museums, for example, sometimes have those coin presser things that will flatten a coin for a souvenir) and they don't get arrested for it.
The comments below have a very comprehensive and punctuated discussion below. Feel free to read them. In addition, I highly recommend you check out the actual law itself, which although does state that one cannot alter money, it adds the term "Fraudulently", referring to the law only being applicable when the alteration of money leads to fraud.

In addition, the laws against damaging or defacing US currency are for US Treasury employees, not average citizens.

waraji (author)assemblyrequired2014-07-10

Nice instructable! There was a guy at my work once who used a Dynafile
(tiny handheld belt strip-sander) to whittle a penny down to the size of
a dime for a nearby soda vending machine. The owner of the vending machine appeared one day in the bosses office showing off the slug and laughing, "this cost me ten cents, but it cost you ten dollars" (wages) :-D

schabanow (author)2015-06-14

Similar idea is to use coin-shaped lithium cell (for motherboard' RTC) as a cache. Or another cell like 18650 for instance. )) Furthermore you can make it still functional, just built in 14500 into 18650 and get ~ 4 cubic cm to hide there your compromising stuff...

Weird activity... o_0 Do you really wanna hide sth? )) Don't you just get rid off it?

paul dito (author)2015-06-14

Fun stuff! Even more fun are the folk who don't understand the law.

JavaProgrammer (author)2015-06-14

this is so cool! I hope you win!

sonisimi (author)2015-04-08


Ploopy (author)2014-08-03


violeta571 (author)2014-02-22

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

Cherrysamurai (author)2014-01-02

That's awesome!!! I hope you win! :D

I do too :D Glad you enjoyed it!

shawno1143 (author)2013-12-28

sorry I thought it was but real good idea. got my vote

Thank you!

karalalala (author)2013-12-24

This is the best thing I have ever seen. Voted!

Thank you, and thanks for your support! I'm glad to see you enjoyed!

mcs320 (author)2013-12-23

Are you making the center thinner or are you removing the edge from the sides? I was thinking if you left a small amount on one side, and then a small tab on the inside, you could have a small watch screw to lock one side on. Harder than using glue I know, and more detailed to create, but just looking at coin compartment 2.0

assemblyrequired (author)mcs3202013-12-23

Do you mean having a tab that would be pressed by the watch screw? That would be cool, as long as I left a channel to keep the other side in line... Very clever idea!

Veda88 (author)2013-12-23

Did you ever buy a coffee with your secret sd card coin? ;)

assemblyrequired (author)Veda882013-12-23

Not to worry, I am proud of this one so I have held onto it! :)

LordBenjamin (author)2013-12-16

Very, very cool, but why would you put anything of value in a piece of MONEY??? Anyone looking to rob you/mooch off a free drink will steal this away from you! Very cool idea, but isn't there anything else you could use?          

Chikpea (author)LordBenjamin2013-12-23

Coin safe things like this were used by the military to give secret messages to one another. You can fit a piece of paper or, in some, a really thin San Disk USB with secret messages on it.

About This Instructable




Bio: 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 ... More »
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