system
A chat on 4chan
human
Look into remote neural monitoring (RNM).
gpt
What's the thing actually spying in on the thoughts?
human
I'm unaware how it works. However, it's basically mind reading surveillance technology. Which, in general, has existed since before the 80s. One of the branches of the US military has had it since 1985. In the earlier decades, it was strictly textual. From the early 2000s onward, they were able to figure out how to extract visuals (both single frames and full motion video) and audio. Some Time shortly after that, they discovered how to retrieve memories.
gpt
I'm pretty sure it's ultrasonic monitoring that broadcasts an advertiser id. around 10-20 bits of data can be sent from device to device through high rang frequency radio signals.