Door Locks – What is This Type of Door Lock Called in English?

If I am inferring correctly what you are describing, it sounds like the "brains" of the system are installed outside with one screw access. That, of course, is an abysmal design. The only thing that should be outside accessible would be the wires to the call button and speaker - all other wiring should be inside-access only.

If you are otherwise happy with the system, you could probably move the components that should not be outside inside, leaving only the wiring needed for the outside components running to the outside box.

This looks to be like a schlange or kwikset lockset commonly found at Home Depot. You can easily re-cylinder this, but it isn't obvious how to get the lock off.

My solution was as follows:

1. Rotate the lever to the vertical position. There will be two screws hidden under it.
2. Remove them, and separate the lock into two halves.
3. The lock-half has a cover on it. Remove it.
4. There's a screw that holds the cylinder in.

You can also get a lock/lever combination, as well as new doorknobs -- in many cases you can re-use the existing deadbolt and striker latch and just change the visible hardware.