I'm working on a phone/tablet app (a musical instrument) whose play mode is full screen. I need a way to open a menu. I don't mind placing a button in one corner of the screen, but I think a normal button might be accidentally pressed when playing the app, and this would be extremely undesirable.
I think requiring a double tap would be accident-proof enough, as would a slide-to-unlock (iOS activation) mechanism.
added: It's a strumming (guitar like) thing, so I think swiping from an edge (like notifications pull down) would be too accident prone. Swipe from a corner along an edge would work, I think, so if there was an established symbol for that...
Are there any existing conventions for this kind of thing?
Added 23 Oct 2013: If there is not existing/established conventions for this kind of thing, I'm inclined to go with a slide-to-unlock (similar to iOS screen unlock) placed along the screen edge. But Apple may have a patent on this, at least in the U.S. I'll have to research the patent.
Added: I've factored out a question specifically about a long-touch symbol: