In my pre-divorce house, it turned out that the flippers who had done the renovations on it did things like put phone and coax jacks in every room that were not connected to anything.¹ Well, there were wires in the wall, but they just went deeper into the wall. In my current apartment, I put in about 50' of Cat6 since the 1920s construction walls kept the wifi signal from reaching from the living room where the fiber drop was to my office off the back of the kitchen. When I buy a house again, one of the first things I’ll do is run ethernet through the whole place.
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1. The other irritating thing was discovering that the light switches were attached only to the faceplate which in turn was attached only to the drywall.