Not only are these collar stays that work but they have a hidden shim in them that can be bent back if you need it. Two types of shim in each pack, one straight and one split pawl so it can easily deal with any situation.
Not just useful for shirt stays, you could secrete them in a book as a bookmark, into the spine or cover of a book. They will easily be hidden in a boot under the sole or hidden in the tongue. Even on a belt!
Its a versatile tool twin pack that means you can carry them daily in a variety of concealed ways.