TL;DR - Sister in law buying a house full of smart junk, she wants to keep it, but is afraid of the previous owner spying on her or gaining access to her home. Can this be mitigated while keeping said smart junk?
My sister in law is in the process of purchasing a home that I would love to have -- it's completely decked out with smart devices. Nest Thermostat, Rain Maker irrigation system, it looked like the HVAC registers were electronic, Hue lightbulbs everywhere, security cameras, ip locks, ip garage door openers, honestly just the works. I'm totes jelly.
Unfortunately, since we don't know anything about the installer other than his previous address, we have no reason to believe that any of it is secure. My first instinct would be to ditch all of it in favor of the traditional dumb devices or new smart hardware; but it's not my house, I'm just being consulted because I'm the "tech guy" for my in-laws. Sadly, I know next to nothing about these types of amenities myself other than the fact that the news keeps on bubbling up about hacked cameras and vulnerabilities in them. Is there anything I can do to attempt to ensure the network security while keeping these devices?
I know if I had full control and were dead set on keeping them, I would want them on a different network than my devices, but beyond that I also don't want anyone to be able to access the house or video feed. I'm mainly asking for home automation specific steps. How is this stuff typically controlled, or accessed remotely?
Note: Of course, the real answer here is "The previous owner had physical access to these devices for who knows how long, there should be no reason to believe they will ever be secure", but my Sister in law, despite the fact that she would never invest in smart equipment on her own (and would make fun of people who do it), just loves the idea of having it.