A dual key lock is a key lock that requires two keys to open. Usually found on drop safes, depository safes, and other type safety deposit boxes at the bank. This is a very affordable and effective lock that requires both keys to be turned before the lock unlocks. The advantage of this lock is that it can require two people to be present before it will open. There are two keys, the “guard” key and the “user” key. The “guard” key is the single key that matches all dual key locks. The lock ships with one copy of this key and it should be turned first. The lock ships with two copies of the “user” key. This key must be turned after the guard key. The user key will turn further (about three eights of a turn) than the guard key (which only turns almost one quarter turn). It is important to realize that the keys must be inserted with the teeth pointing either up or away from the hinges (depending on the safe model and the bolt work configuration).Many keys come with a code on them. Please make sure that you keep track of the code written on each key and that you use the correct key with the correct safe. It is somewhat hard to find a locksmith that can duplicate these keys in some small towns. It is referred to an S&G Blank and it is quite common.