Spoiler
1938
The Radio Nurse was the first electronic baby monitor. Manufactured by the Zenith Radio Corporation, it went on sale in 1938. The product was developed by Zenith executive Eugene F. McDonald, and designed by Japanese-American sculptor and product designer Isamu Noguchi.
Although the product was manufactured for only a few years, it has been acclaimed for its design. It is still in demand as a collectible and is in many museum collections.
Noguchi also designed the Noguchi table.
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Was going to say '53, but I guess we had radios well before then.
Looked very art deco, that's why I went with the early 30s.