It is likely to have either been the recording level indicator on an old valve reel-to-reel tape recorder, or the tuning indicator on an old valve FM radio.

The whole point of the Magic Eye tube was that it was cheaper than an analog meter. So it was the consumer-grade replacement for one. On pro gear, you'd find a meter movement and pointer, which is harder to make than a vacuum tube.

In "The Day the Earth Stood Still" (1951, not the remake), when the visitor goes into his flying saucer and powers up a communicator to report to HQ, there are two huge Magic Eye tube like devices. So back then it was a cliche for "radio". Start at 55 minutes.

[1] https://archive.org/details/day-the-earth-stood-still-1951

thank you.

I suspect it must have been a radio. I remember it said something about eye, but was always dark.