FBI Guide to Concealable Weapons: The FBI has issued a fascinating document for law enforcement officers demonstrating ways that someone could sneak a weapon past a security checkpoint, such as at an airport or courthouse. The document includes images of what these weapons would look like to the naked eye as well as with an x-ray machine. These are all commercially available. Many of these are legitimate tools, but some of the items are quite ingenious and clearly designed to disguise their true nature as weapons. (Warning -- lengthy .pdf file.)