A switchblade is simply a knife which can open very quickly because the opening mechanism is powered by mechanical energy stored in a spring. Inside the handle there is a piece of spring steel which wants to bend. The end of this presses against the blade (at the lowest part, near where the handle connects with the sharp part). The thing stopping the spring from pushing the blade out is a small metal pin that fits into an indentation in the blade. Pressing the button moves this pin out of the way, and the blade opens quite quickly.
To correct the possibly popular opinion that switchblades are double edged (two writups previously here mentioned this as a standard feature). They are not. At least, both of mine (which I got in completely different places and were made by different companies) are single-edged. One has a spot where I could (theoretically) sharpen it to a double edge, but the other looks pretty much like a normal knife blade (if on the long and thin side).
Switchblades are not illegal to own in the United States (as far as I am aware). However, carrying one on the street is probably illegal, as is bringing one across state lines in order to sell it (in the United States, this is apparently a federal crime). It seems you can sell them legally on reservations, or at least you can get away with it without too much hassle. I think it's pretty stupid that there are so many laws about this, actually. I own a double-edged fixed blade knife that will hide inside my jacket pretty much invisibly, and I can get access to it in less time than it takes me to pull a switchblade out of my pocket and open it. I imagine it is also illegal to carry concealed, but at least I could go into a regular store and buy it.
Any switchblade you see in a store (in the US) is a fake, a regular folding knife made up to look like a switchblade. You need to have a special license (only given to cops and military people) to buy the real deal - unless you know the right people. <g>
As Arathil noted in a writeup that used to be here, switchblades are not that great for serious knife fighting. Once, I tried to open one of mine, and the mechanism was slightly jammed, so it failed to open. Then all of a sudden it came loose and snapped open, and in my surprise I nearly dropped the (now open) knife onto my foot. Yes, they look cool, and you see them in all the movies, but trust me, it's not the ideal tool for this particular job (personally, I'd take a machete - but my personality tends towards overkill.)
Someone at the Baltimore Tattoo Museum told me that if you have 3 or more switchblades, you're a collector. I asked him what you were if you only had two. His response: "A psychopath". (This really happened, but nevertheless, TWAJS).
Places to get switchblades (for the interested):
- Indian reservations
- From a rockabilly guy named Vince, outside a tattoo parlor (really)
- Probably certain areas of Europe, but I don't know for sure.
- According to martinborman, they are easily and legally available in Panama.
Please /msg me about any other good places to get switchblades, I would like to provide this as a service to e2's knife-collecting/using users.