Yesterday, the ELFON UNIFON OP-U7 intercom was installed in the stairwell and only the keys are to be distributed to the residents without the possibility of entering the code, because in other stairwells the codes are passed on and therefore the intercoms do not fulfill their purpose, but I would still like the codes to be entered. I would rather enter a code than make a second key and the key can be lost. Is it possible to program the intercom so that it can be opened with a code, but so that I can program it myself without the knowledge of other people because they would not agree. Almost everyone wants a key and I prefer a code. Is there a universal code that opens all intercoms?