What does the code in the intercom key consist of?

Question

Burglary protection

So. The question was asked incorrectly.
Let's start with what I know. At the factory, an access code is entered into the key. This access code fits into the intercom. When the key contacts the intercom, the key transmits some code to the intercom. Actually the question of what does this code consist of (numbers and letters)? Unfortunately, this is all that I could dig up on the Internet about this.