Note to people outside of the US who are worried about this:
The rest of the world uses 3G/4G modems in their smart meters, they are usually also connected to a different APN than generic mobile data. Sometimes multiple meters are connected to a central hub with a physical wire (in apartment buildings for example). The hub is then the only gateway to the internet.
The hack in question is only viable because of the weird way US smart meter collection is done.
US Smart Meters use RF to shout out their values everywhere like an RF beacon. A power company vehicle drives around the neighbourhood, collecting the values, storing them and moves on.
Source: I did smart metering software for L+G.
> A power company vehicle drives around the neighbourhood, collecting the values, storing them and moves on.
What the fuck
It's like the meter man visiting your house, but now they no longer have to enter. Isn't it wonderful? If I lived in the US, I'd immediately try to hack up a small Arduino project to read out my neighbours' energy usage.
The result is a smart home energy monitor that doesn't require any clamps near the electrical panel, and it exactly matches the usage for which I'll be billed.