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...)

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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.
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sonisimi1 month ago


Ploopy9 months ago


shawno11431 year ago
this is a felony
assemblyrequired (author)  shawno11431 year ago
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.

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

violeta5711 year ago
this is awesome! I can imagine exchanging secret messages with my best friend with this
theegghead1 year ago

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

hope you win the contest!

assemblyrequired (author)  theegghead1 year ago

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

That's awesome!!! I hope you win! :D
I do too :D Glad you enjoyed it!
shawno11431 year ago
sorry I thought it was but real good idea. got my vote
assemblyrequired (author)  shawno11431 year ago
Thank you!
karalalala1 year ago
This is the best thing I have ever seen. Voted!
assemblyrequired (author)  karalalala1 year ago
Thank you, and thanks for your support! I'm glad to see you enjoyed!
mcs3201 year ago
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)  mcs3201 year ago
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!
Veda881 year ago
Did you ever buy a coffee with your secret sd card coin? ;)
assemblyrequired (author)  Veda881 year ago
Not to worry, I am proud of this one so I have held onto it! :)
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?          
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.
assemblyrequired (author)  LordBenjamin1 year ago
Who would want to steal 25 cents? Besides, I think the international spy agencies that used this device (KGB, etc.) would have thought of that, but they made them and used them anyway. Besides, the goal here is to be discreet, and a coin does that quite well. Yes, there is many, many other things that could be used, but I can't think of any of them that are any more James Bond-ish than a compartment in a coin-- It's a classic! In addition, the coin is the most common device of the right size that I could find. Thanks for your comment.
True, I suppose. Good idea, though!
assemblyrequired (author)  LordBenjamin1 year ago
Thanks, glad you enjoyed!
Are you aware that it violates federal law to deface currency?
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...
But it's not illegal *yet*, and that's all that matters.
Are you aware that it's illegal to sing happy birthday in public without paying royalties to Warner Chappell?
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.
assemblyrequired (author)  MajorWebUser1 year ago
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.
All of your ibles have one problem... They are too awesome!
Absolutely terrible, isn't it :)
Yeah, it's a real problem
Too bad I may never be able to fix this problem... :D
Glad to see you enjoy them!
presto021 year ago
thanks, that suff is nice to know.
assemblyrequired (author)  presto021 year ago
Yup! :D
kjlpdx1 year ago
a router could do this cutting quite clean and easily.
assemblyrequired (author)  kjlpdx1 year ago
If only I had one! One of my goals is to create Instructables that people with a basic tool kit could pull off, and so I wouldn't have made one forcing people to use tools they might not have, preventing them from trying this. However, a router would make this easier if you could get one small enough for a coin. he closest thing to that is a Dremel, and you may remember that that is what I used.
mcrawford21 year ago
Actually, it is no longer illegal to deface u.s. money
Actually, it is illegal. Based on this information. It is legal to deface PAPER money, but not COINS! As for the comments that it's "only 75 cents". Go ahead, piss the Feds off. People get legal action taken against them for all kinds of stuff. I'm just sharing the info. Have fun.
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