Your comments

Is any kind of switch that changes the brightness of a light considered a dimmer/bad? My parents have a light switch (very old) that has a halfway-on position, and the ceiling fixture goes from off, to on, to brighter on. I imagine the lightbulbs in that fixture are old incandescents, but don't know if they're 2-way bulbs.

Shaun, are you referring to PLC/power line communication? My smart meter uses that method, rather than  the wireless transmission most people think they have, and according to this article/website ( ), TWACS (Two-Way Automatic Communication System) cannot be blocked or filtered: "There are no filters available to block these low frequency signals.  The TWACS system is specifically designed to go right through obstacles, including isolation transformers.  Filters designed to block high-frequency dirty electricity have no effect on the lower TWACS-frequencies.  This includes the simple Stetzer filters, as well as more sophisticated filters." So I'm pretty much screwed in terms of dirty electricity in my house. Maybe I should have put this in a whole other question on the forum, but you made a reference to PLC and the subject was filters.... Thanks!