I decided that for Starcaster II, the spy headquarters needs a network of speaking tubes. Here's a brief explanation of speaking tubes I found online:
A normal installation had a removable whistle plugged into each end. To initiate a conversation Person A removed his whistle and blew down the tube, sounding the whistle at the other end. Person B then removed his whistle, and talking could begin. Hence the expression, still current in Britain, "I'll get him on the blower" when a telephone call is meant.Naturally Mr. Felding, the Commissioner of the Starcaster Corps, will have a network of speaking tubes that all lead to him. And naturally, he will keep the whistle removed at his end, because that's just the way he is. And naturally, a bunch of people will constantly be sneaking into his office in order to use the speaking tubes when they can't find someone. Down in the workroom, people will quickly get tired of the tube whistle and may even "lose" it from time to time. It will drive the dog--who belongs to Tory but stays at HQ because HQ has a larger garden--insane, and I'm thinking that the dog really needs to start howling whenever the whistle sounds.
Such systems appear to have been quite common in homes and offices, though very little information about them, and very few references to them, seem to remain today.
Low tech. It's fun stuff. It makes my imagination run wild. I have as one of my reference books a copy of Isaac Asimov's Chronology of Science and Discovery. Sadly, it appears to be out of print, but some people are selling used copies at Amazon. One is even billed as a collector's item!