If I buy more than one set, are they keyed alike?
No, each set has its own keys (3 copies).
Will it work on a metal door?
It depends on the thickness of the door. It is ok if your door is 1-3/8" thick or 1-3/4" thick.
Can I lock the door without using the key when I leave the house?
No, before you leave, make sure the door is locked with the key. In this way, you will not lock yourself out by forgetting to take the key with you.