You don't need to exploit sensors. If a compromised device is connected to the internet (because the vendor app requires it to set up and control), you can use it as a part of botnet with a nice residential IP address.

Shopping in the US, these have entirely replaced zigbee and other sensible mesh-based options at hardware stores like Home Depot and Lowes. The only exception I can find is Phillips Hue, and those seem to be slowly getting phased out with (sigh) a new "hubless" (requires wifi) series.

I run my home automation network entirely offline, so anything that needs the internet doesn't get added to my cart. I just do not trust the security of these IoT vendors at all, and refuse to have their nonsense cluttering up my limited network bandwidth and causing unknown problems.

(Edit: maybe not obvious, this is in the "smart bulbs" product category. Regular bulbs are still much more common on store shelves, because why fix what isn't broken? Most people don't need to automate their light bulbs.)