Just got a new toy in the mail today. An eBay purchase - a Sezam lock from Poland, unused in box!

The lock requires a key in the middle, and the outer four 'keyholes' are for entering the combination. 10 numbers, 4 fields = 10,000 possible combinations. The tip of the key can be used to enter the combination, then the key is used to turn the lock. If the wrong combination is entered, it feels exactly as if you have the wrong key.

Key turns like this when the correct combination is entered.

Here are the keys. The top one is for changing the combination. The notch on it is not necessary, in case you were wondering. The bottom three are all the same, and are used in the center keyway to operate the lock.

To change the combination (from the factory is 0-0-0-0), enter the current combination, press in on any of the four combination buttons. While pressing on the button, turn the key. When the key is at the proper position, the button will drop down into the lock.

Put the tool (the larger key-like thingy) into any of the code fields

Press it in until it stops moving inwards

With it pressed in, turn it to the number you want at that position.

Remove the tool. The button should pop out. If not, turn it slightly until it does.

Repeat for all four code fields you wish to change. Even changing one number makes the key no longer turn with the old combination.
Here is the bolt mechanism. Unlocked

Locked from the inside (the handle at the top is lifted, then slid over).

And fully locked.

Technically, the above picture (fully locked) is not possible with this lock unless somebody inside AND somebody outside both lock the lock from their side. The top bolt can only be thrown from the inside, and the three lower bolts can only be thrown by the key from outside! Guess they thought you did not need full security if you were inside your home???
Hope you like it!
Gordon