First thing I do when I get a smart appliance is scan it with nmap. This has revealed some interesting Easter eggs, like my Davis instruments air quality sensors having a local REST API.
Doing the usual scan against my GE washer and dryer shows that port 53 is listening. What could that be for? Is there a way I can at least query their status locally or something?
When I got the washer and dryer I was excited about the smart home features because getting an alert when my laundry is done or starting the washer remotely so the clothes are done when I get home are genuinely useful features. However, last time I checked the app none of that was available, so I just have these Trojan horses in my home spying on me with no benefit in exchange. Their app wanted my freaking mailing address when I signed up for their mandatory account, so the features mentioned above are the least they could offer in exchange for my digital soul. But I digress.
My fridge is in a similar situation. It commits the additional cardinal sin of ONLY being controllable via the app, with no on-board temp or filter status indicators whatsoever.
Most appliances connect using a cheap microprocessor like an ESP-32 which provides both WiFi and BLE.
If there’s a DNS server running, it’s usually for mDNS/ZeroConf service discovery. Usually so it can easily get provisioned via a smart speaker or hub.
More details here: https://circuitlabs.net/dns-server-and-dns-sd-implementation/