Ballpoint pen knife
A ballpoint pen knife is a multi-tool pocket knife consisting of a blade concealed inside an ordinary ballpoint pen. The blade, typically 2 to 5 inches (51 to 127 mm) in length, is usually hidden. They first appeared as custom-made pens from various custom knife makers before being mass-produced by production companies.
Pen knives such as these are designed for self-defense due to their ease of concealment. Their small size renders them impractical as weapons in elaborate combat, but their slim profile allows them to cause great harm in close-range combat with an element of surprise.
A knife of this type can also be used as a standard letter or package opener. Pens crafted with survival type blades can also be used for peeling fruit and vegetables, cutting meat, and carving or shaping wood. They come in many versions, including variants with special purpose razors for shaving.
Kinds of blades
All ballpoint pen knives come with straight blades, which are easier to conceal than curved blades. These 2-to-5-inch (51 to 127 mm) blades are fixed to the topmost part of the pen, hidden inside a hollow cap, serving as both the pen's end and the knife's sheath. Common blades may be the single-edged thrusting type or the double-edged stiletto type. Blades can be razor-sharp or deeply serrated for use in a range of situations. Swiss Army Spectrum Series released their S.A.S.S. Ballpoints, which look and function like regular ballpoint pens. They come with an array of foldaway blades and tools including knife, scissors, file, opener, screwdriver and battery-powered light.
Ballpoint pen knives, because they allow a knife to be disguised as an inoccuous object, are subject to restrictions or prohibitions in some jurisdictions. For example, in North America are not available for sale in California  or Canada.