I mostly agree.. there’s a couple of very specific scenarios where maybe something like knockd makes sense I think but they are all scenarios where you’re doing things covertly, not as a general authentication mechanism.
As a side note I just happen to be reading a book at the moment that contains a fairly detailed walkthrough of the procedure required to access the Russian SVRs headquarters in New York in 1995.
Think of this as an analogue version and in no way a perfect analogy but it does include a step that has more or less the same security properties as this… anyways here’s a relevant quote:
“After an SVR officer passed through various checkpoints in the mission’s lower floors, he would take an elevator or stairs to an eighth-floor lobby that had two steel doors. Neither had any identifying signs.
One was used by the SVR, the other by the GRU. The SVR’s door had a brass plate and knob, but there was no keyhole. To open the door, the head of the screw in the lower right corner of the brass plate had to be touched with a metal object, such as a wedding ring or a coin.
The metal would connect the screw to the brass plate, completing an electrical circuit that would snap open the door’s bolt lock and sometimes shock the person holding the coin.The door opened into a small cloakroom. No jackets or suit coats were allowed inside the rezidentura because they could be used to conceal documents and hide miniature cameras.
SVR officers left their coats, cell phones, portable computers, and all other electronic devices in lockers. A camera videotaped everyone who entered the cloakroom. It was added after several officers discovered someone had stolen money from wallets left in jackets. Another solid steel door with a numeric lock that required a four-digit code to open led from the cloakroom into the rezidentura.
A male secretary sat near the door and kept track of who entered, exited, and at what times. A hallway to the left led to the main corridor, which was ninety feet long and had offices along either side. ”
Excerpt from
Comrade J by Pete Earley
As another funny side note… I once discovered years ago that the North Koreans had a facility like this that they used to run a bunch of financing intelligence operations using drugs in Singapore where I was at the time and thought it would be funny to go and visit. It was in a business complex rather than a dedicated diplomatic facility from memory. But as I recall it was a similar scenario of unmarked door with no keyhole.