New key - game already in library - still works?

No. If you already have the game in your library. STEAM doesn't check whether the key is still valid or already used.

No, it will still be available for others.

No. It will work for others without a hitch.

if you already have it you can't activate the key. it is still good, you can make a giveaway. :)

Ok thanks everyone :)

Yeah, though you can't find out if it's still good or if it has been activated already by someone else. It sucks they don't do something so you can check if the key is used without activating it yourself.

no