An assisted-opening knife can be legally manufactured, sold and possessed under federal law. Although they are often confused with switchblades, assisted-opening knives differ from switchblades in many ways. One of the ways the two knives differ is that while switchblades are prohibited, assisted-opening knives are perfectly legal.
In 2009, the Federal Switchblade Act was actually revised and clarified so that assisted-opening knives would not fall under the prohibition of the act, which only outlawed switchblades. The change made sure that the Federal Switchblade Act does not apply to:
“a knife that contains a spring, detent, or other mechanism designed to create a bias toward closure of the blade and that requires exertion applied to the blade by hand, wrist, or arm to overcome the bias toward closure to assist in opening the knife.” (Source)
Even though spring assisted-opening knives are not prohibited by the federal government, you cannot carry assisted-opening knives, or any others, into areas where knives are generally prohibited, such as courthouses, federal buildings, schools and airports.
Again, the federal law does not prohibit assisted-opening knives, but states have interpreted the law in different ways and often have other restrictions. For example, in some states, any knife including assisted-opening knives with a blade length of more than 2.5 inches is illegal to carry. You must refer to your state laws to determine whether your knife meets state requirements, but rest assured that assisted-opening knives are legal in all 50 states.
Since state knife laws are constantly evolving, thanks to organizations like Knife Rights that keep pushing through legislation that clarifies the legality of assisted-opening knives and removes arbitrary restrictions, it’s always important to look at the most up-to-date information for your state.