Couldn't he just use a door to indicate the same status? Door open = okay to come in. Door shut = no interruptions.

He seems eager to create additional work for himself to come up with a solution when there isn't really a problem. I wonder what else in life he is going to come up with an elaborate solution for (introducing many new potential points of failure) when the obvious solution has been in front of him the whole time. Would you really want to work with a guy like that? Would you want to pay him to solve problems for you?