Clive Robinson • December 16, 2008 3:52 AM

Two things you want to do with it ifyou want to reduce the chance of detection.

The first is make sure that with the SD card it weighs just under the correct amount (if you are going to pad with lead make it as a foil or ring to keep the coins balance).

Secondly fill the remaining space with a small amount of silicon rubber to stop the SD card moving around and to help make the coin not sound hollow.

as for the coins of other countries the some of the Euro coins are very good as is the UK 2 Pound coin as these consist of an inner silver coin with a large outer gold rim.

These would be spot on for machining and would still sound like they should do, and of course they have a natural seam so that removes that little problem as well 8)

Clive Robinson • December 25, 2008 3:18 PM

@ markm,

A festive winter(?) solstice to you.

With regards to lead in coins to “make weight”.

First of I’m not from the US and it’s coinage is not that well known to me, and on my infrequent visits it has been a source of anoyance to me (I have little idea what a nickle etc is for instance) primarily due to the lack of identifiable indications.

However in Europe coins have been made from all sorts of metal alloys in the past some quite light. Also some more modern European coins such as the UK 2quid coin (2 pounds) is quite thick (it has writing around the edge as part of the milling). So the scope for doing this may well be greater than for US coins.

Further although lead was once a commonly available metal (considerably less so these days) with a moderatly high density, there are others with higher densities still and better mechanical charecteristics.

Uranium (~19) being one that is not overly difficult to obtain (I once owned several tons of the stuff in the form of a keel weight, and you will also find it in some comercial jet aircraft as counterbalance weights).

There are others such as Osmium (~22) but as you work your way up some have some decidedly unplesant charecteristics and their availability is close to zero for the common man (not so Governments as the Polonium 210 assasinatioon in London showed).

The basic point remains, if you can find an appropriate volume/mass trade off especialy with a metal/alloy of high structural strength then the coin is considerably less likley to be noticed as being “odd” in the company of like coins.

However there is possibly a simpler way to do it which is just mount a hollow coin in a necklace or pendent. As has been pointed out such “keep sakes” or “lucky charms” are not exactly uncommon.

But to be quite honest there are easier places to hide a micro SD card. As I have noted in other postings a metalic packet of “chewing gum” is good for many reasons. Other simple places such as a Zippo lighter, or the metalic button on a blazer have been used in the past.

Then there is the collar of a “button down” dress shirt that has studs or metalic buttons simply slide the stiffener out and drop the SD card in. There is also the crotch seam of jeans with the “501” rivit, the fold between the upper and tounge of “trail boots” “walking shoes” which have metalic studs or lace in zippers (all of which I have had in my luggage or worn through customs since 9/11)

Also have you looked at metalic fasteners on older camera straps, the design of wooden and plastic coat hangers. With a blob of soft glue it can be stuck inside the metalised spray top of quite a few aftershave bottles. The list goes on and on and on

Which is why in reality a hollowed out coin is of little use except for “passing” in an apparently innocent manner (and a stick of gum is almost as innocent).

To be quite honest to “carry” it I would stick a micro SD card in my wallet in amongst the “Chip-n-Pin” credit cards. It is fairly easily explainable as a place of safe keeping along with a spare mobile phone SIM card or two. And you would expect the chips in the credit cards to effectivly hide any signiture a micro SD card is going to give out to an airport grade scanner etc.

And when have you ever seen somebody who has had their laptop taken for “checking” ever have their wallet turned out and properly searched?