One way to store your spare key?

Genius

Um

Trying to be smart but failing

Really ?

If you need your spare key, that would imply that you have lost your other key, therefore there would be no way to get the spare key. In short, this is not genius or smart, it is quite dumb

OK guys guys guys... who says that key unlocks that lock? It actually IS genius if it's say, a spare front door key.