A three-number combination lock has a million possible combinations; a four-number lock has a hundred million. If you suspect that your combination has been compromised, a simple five-minute change will render the safe secure against most attempts to open it. Changing the opening procedure on a good quality combination lock fitted with a change key on the inside of the safe, and a change index on the combination dial, is a fairly simple procedure.
Open the safe and turn the handle clockwise to lock the door open. Spin the combination dial a few random turns to set the lock.
Turn the combination dial counterclockwise four full revolutions. Stop on the fourth revolution when the first combination number is perfectly aligned with the "open" downward pointing index arrow located at the 12 o'clock position on the outer rim of the dial.
Reverse direction and rotate the dial three clockwise revolutions. Stop on the third revolution when the second combination number is aligned with the open index arrow.
Turn the dial counterclockwise twice. Stop on the second revolution when the third combination number reaches the open index arrow.
Rotate the dial slowly in a clockwise direction. On the second revolution when the 95th mark approaches the index arrow, the lock bolt will retract and the dial will stop turning. If it doesn't, you have dialled the combination incorrectly and must start again from the beginning.
Remove the old combination. Insert the change key into the keyhole located on the inside body of the dial mechanism. Turn the change key counterclockwise a quarter of a turn to put the lock into a neutral position.
Dial the new number by repeating Steps 2 through 4. However, instead of stopping on the arrowed index mark, stop on the change index mark located either at the 11 o'clock or the 1 o'clock position. The change mark is usually a straight line, but it could be a circle, depending on the lock manufacturer.
Test the new combination. Leave the safe door open during the test. Lock and unlock the door several times with the new combination. Do not write the combination down--commit it to memory for security reasons.
Never use ages or birth dates associated with friends or family members. Rather use a random number generator or a pair of dice to select your new combination numbers. The first number in the new combination must be greater than 25.