Never use a deadbolt that is operated by a key on both sides of the lock, commonly refered to as a double-sided deadbolt. These locks should be prohibited by law. I always ask customers who request them, “What is more valuable, your television or your life?”. In the case of a fire, these locks can lead to your death. One manufacturer does make such a lock that uses a key on the inside with a knob on the key. This lock also retains the inside key unless you use a key from the outside. The theory behind this is logical, but if anyone uses another point of entry and forgets to put the key back in, an extreme risk has been created.