The law in Wisconsin is pretty vague:
Wisconsin - 941.24. Possession of switchblade knife. (1)
Whoever manufactures, sells or offers to sell, transports,
purchases, possesses or goes armed with any knife having a
blade which opens by pressing a button, spring or other
device in the handle or by gravity or by a thrust or
movement is guilty of a Class A misdemeanor...
[Note: The wording of this statute is different from all other state
switchblade statutes.]