A port of Probe by BR Law for the ZX81 published in Your Computer, December 1982 to the BBC Model B, Master 128 and Acorn Electron range of microcomputers.
Released 16th May 2020.
This is a simple puzzle game with limited replay value. The presentation has been slightly modified.
The program is distributed as a bootable DFS format SSD and the latest version can be downloaded from the Resources menu.
For instructions, please refer to the original magazine article, here.
You almost certainly don't want to select the training / beginner option as that reduces the already limited game play to zero.
You just enter the key and lock numbers when prompted. To remove a key from a lock, you just insert the key into a different (vacant) lock.