[DJ Frisat]

”A TV without a microphone cannot listen in.”

I wouldn’t state this as an absolute. I’d say that such a set is less likely to ‘listen’, but it can be done. A conventional ‘loudspeaker’ - the device historically used to play audio in televisions, radios, cassette players, etc. - can also be used as an input device, aka a microphone. This may also be the case with newer audio transducer types, but I’m only talking about speakers.

For this to work efficiently, it would require the set to be designed, or modified, to function in a bidirectional mode.

Never say never! 😉

[GingisK]

My TV does not have uplink capability.

[Elsie]

It has an antenna.

A BURST of info being transmitted from it would never be noticed at all by those sitting in front of it.

heck, the early closed caption wording was encoded in the non-visable portion of the tv signal.

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The closed captioning system was successfully encoded and broadcast in 1973 with the cooperation of PBS station WETA.^[2] 

As a result of these tests, the FCC in 1976 set aside line 21 for the transmission of closed captions. 

 

  https://en.wikipedia.org/wiki/Closed_captioning#Technical_development_of_closed_captioning

 

https://en.wikipedia.org/wiki/EIA-608