Do you have the source code to firmware on the chip in the pants? Can you install a custom version? That would be consistent with the FSF's viewpoint. They want the user to have full access and control over the software he uses in all devices he uses.
https://stallman.org/stallman-computing.html
However, if I am visiting somewhere and the machines available nearby happen to contain non-free software, through no doing of mine, I don't refuse to touch them. I will use them briefly for tasks such as browsing. This limited usage doesn't give my assent to the software's license, or make me responsible its being present in the computer, or make me the possessor of a copy of it, so I don't see an ethical obligation to refrain from this. Of course, I explain to the local people why they should migrate the machines to free software, but I don't push them hard, because annoying them is not the way to convince them.
Likewise, I don't need to worry about what software is in a kiosk, pay phone, or ATM that I am using. I hope their owners migrate them to free software, for their sake, but there's no need for me to refuse to touch them until then. (I do consider what those machines and their owners might do with my personal data, but that's a different issue, which would arise just the same even if they did use free software. My response to that issue is to minimize those activities which give them any data about me.)
That's my policy about using a machine once in a while. If I were to use it for an hour every day, that would no longer be "once in a while" — it would be regular use. At that point, I would start to feel the heavy hand of any nonfree software in that computer, and feel the duty to arrange to use a liberated computer instead.
Likewise, if I were to ask or lead someone to set up a computer for me to use, that would make me ethically responsible for its software load. In such a case I insist on free software, just as if the machine were mine.
As for microwave ovens and other appliances, if updating software is not a normal part of use of the device, then it is not a computer. In that case, I think the user need not take cognizance of whether the device contains a processor and software, or is built some other way. However, if it has an "update firmware" button, that means installing different software is a normal part of use, so it is a computer.