"The telescreen received and transmitted simultaneously. Any sound that Winston made, above the level of a very low whisper, would be picked up by it; moreover, so long as he remained within the field of vision which the metal plaque commanded, he could be seen as well as heard. There was of course no way of knowing whether you were being watched at any given moment."
One Rob Braxman discusses a recently activated capability in the devices if you click the above quote. And I might as well throw in another link to the 1984 film production of, well, 1984:
https://odysee.com/@notanotherbrick:f/1984-(1984):5