This ad from the August 1918 issue of Electrical Experimenter magazine shows an interesting code practice set which appears to be a combination key and sounder, for the low price of 25 cents (plus six cents for the catalog the company wants to get in as many hands as possible.

The ad contains the copy: “Impossible–you say. Quite so.” I’m still not sure exactly how it’s supposed to work. My best guess is that there’s another contact not visible behind the front binding post, and the key is wired in series with the coil. The sounder and the key would have to be able to move independently, which I guess is possible if it’s flexible enough and the center mount is firmly attached. Hooked to a battery, the sounder would then click whenever the key is depressed.

According to the ad, two such units can be connected, with a range of up to six blocks. This would require the key to be shorted out, and there doesn’t appear to be a convenient way of doing that, other than perhaps just holding down the key while receiving.

The ad reminds readers that telegraph operators are scarce, and that Uncle Sam needed thousands. For the entrepreneurially minded young men, the ad points out that boys are ordering 6-25 of them and selling them to their friends like hot cakes for 30-40 cents.

Even though the sounder would be most useful for learning American Morse for use on a landline telegraph, the text around the key is in International Morse, and reads:  EICO NY.