The "pen" resembles an ordinary ballpoint, but when clicked it releases a spray of fast-acting tranquilising fluid, which can be used to contaminate enemy food or drink.
In "Chuck versus First Class", Chuck is given the pen by Daniel Shaw, and attempts to use it to knock out Hugo Panzer on a plane flight to Paris. Due to the unusual pressure inside the cabin, the pen malfunctions at first, but eventually Chuck is able to use it to knock Panzer out when he sprays it directly into Panzer's mouth. However, it has significant disadvantage. Unlike tranqulizer dart, its victim is unconcious, but not very deep so it can be waked up by causing it pain (slap, electricity etc.).