You had to live – did live, from habit that became instinct – in the assumption that every sound you made was overheard, and, except in darkness, every moment scrutinized.

George Orwell

1984. Part 1, Chapter 1. We are introduced to how intrusive Big Brother is. Behind Winston Smith’s back he he is hearing the voice from the telescreen, which is babbling away with Party propoganda but can also transmit and receive simultaneously.