The Firearms/Toolmarks Unit of the Federal Bureau of Investigation has put out an amazingly useful guide to concealed weapons:
In the wake of the September 11, 2001, airline hijackings the FIREARMS AND TOOLMARKS UNIT of the FBI LABORATORY has started a collection of small and easily concealed knives. This is the first installment of a continuing effort to collect and distribute information on knives that otherwise may be dismissed as non threatening items. Many of the knives in this collection were commercially purchased and typically can be bought for less than $20. Some of these knives are common items found in most homes and offices. You will notice also that some are made of a plastic material, making them less likely to be considered a weapon. Each of these tools was designed to cut and is fully functional in that respect. Whether used to cut paper, cardboard, or other material, these knives should be treated as potentially dangerous weapons. Each knife is shown with an accompanying scale for size reference and many include an X-ray photograph to show how these weapons might appear if placed in luggage and passed through a scanning device.Guide to Concealable Weapons, published by the Federal Bureau of Investigation, 2003
Guide to Concealable Weapons 2003
In the wake of the September 11, 2001 airline highjackings, the Firearms and Toolmarks unit of the FBI Laboratory started to compile information on small and easily concealed knives. This is the first installment of a continuing effort to collect and distribute information on knives that otherwise may be dismissed as nonthreatening items.Guide to Concealable Weapons, published by the Federal Bureau of Investigation, 2003
Not only will they show you were to conceal the weapons:
But they'll show you what weapons you could conceal. It's a virtual shopping catalog, albeit missing Website URLs and prices. You get to see each weapon closed, open, and even an x-ray view. When a weapon is made from ceramic or plastic, and thus immune to magnetometer screening, the guide will tell you. Now, this isn't anything you couldn't get from the catalogs or online, mind, so there's no great secret here. The advantage is that the FBI has collected it for you in one handy place.