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Hollow coin
Concealment device

In spy tradecraft, virtually any common object can be converted into a concealment device. Take for instance this ordinary coin that has been machined in such a way that it can be taken apart, revealing a tiny secret storage compartment for small objects, such as a piece of microfilm [1].
The 50 Euro-cent coin shown here is identical to any other 50 Euro-cent coin in every respect, except for the fact that it can be taken apart. It is constructed from two different coins of which a small storage compartment has been milled-out at the center. Once pressed together, it can not be distinguised from any ordinary coin.

As is is a tight fit, it will not open accidently. In order to get access to the secret internal stash, the user needs a special aluminium ring with a narrow rig on the inside. The coin is inserted in this ring and then tapped firmly on the table.
32GB Micro-SD memory card inside a 50 Euro-cent coin

After a few attempts, the coin will come apart and reveal its inner secrets. During the Cold War, coins like this were used for hiding pieces of microfilm on which secret documents were copied. The coin could be carried in the owners wallet and would not be discovered during a search.
Today, the coin could easily be used to hide a computer chip, like a Micro-SD memory card. Such memory cards can hold thousands or even millions of secret documents. If we assume that one A4 page of text takes 4KB, the 32GB memory card shown above can hold 8 million pages! And even if the pages contain images, there is still room for many thousands of them.

The hollow Euro coin shown above is a high-quality reproduction made by Dereu & Sons in the US [2]. It comes with the special aluminium rigged ring that is needed for opening the coin.
Hollow coin (opened)

Coins like this can be odered on the internet and can still be useful concealments in today's world. It can be hidden in your appartment without attracting any attention, and it is unlikely that it would ever be found, even if the appartment was thoroughly searched. And for those who live outside of Europe: this type of concealment device is also available as a UK-Pound and US-Dollar (half or quarter dollar). Naturally, Crypto Museum would not advise any illegal use of this device.
50 Euro-cent coin 50 Euro-cent coin with opener 5- Euro-cent coin in the opener ring Tapping the point on the table After a few attempts it will open Opening the 5-cent coin Open 50-Euro-cent coin with 32 GB Micro SD card 32GB Micro-SD memory card inside a 50 Euro-cent coin
Ordinary quarter dollar coin At first sight: an ordinary quarter dollar coin Rigged ring used for opening the coin Tapping the coin, so that it comes apart Hollow coin (opened) Inner side of the coin Close-up of the rigged ring 32GB Micro SD card inside a 50 cent Euro coin

  1. Wikipedia, Dead drop
    Retrieved October 2014.

  2. The Dereu & Sons Manufacturing Company, 50 Euro-cent concealment device
    Retrieved August 2015.

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Crypto Museum. Created: Friday 14 August 2015. Last changed: Sunday, 15 January 2017 - 09:01 CET.
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