Bestaa is correct in that they greatly diminish the propagation of radio waves. They are not perfect faraday cages but a lot of the better insulated walk ins are very difficult to get radio waves into them. Cell service, walkie talkies, WiFi, GPS.
I’ve never walked into a walk in where my service wasn’t significantly impacted.
Not sure what you’re on about.
This has got to be only the most common plugs around the world.
I’m only familiar with US standards but this doesn’t seem to cover our other plugs for higher voltages.