In the first season of Stranger Things, communication between the real world and the upside down seems to have some interesting properties. Initially communication only seems possible as echoes of voice from the real world to the upside down (and this is demonstrated several times, but the reverse is not possible except at near breaches/gates).
Eventually it is shown that Eleven can use radios to hear things in the other side and then Joyce Meyers develops a method for Will to communicate as well. However,
- How did Will know the specific locations for the different letters?
In the final episode of season 1 we see that recent changes such as the bear trap or any of the Christmas lights are missing from the Meyers home within the Upside-Down. Joyce Meyers doesn’t say anything out loud while writing the letters (and anything spoken would be extremely hard to localize that well).
- Did Will even know he was turning lights on?