> a $5 microprocessor with just enough intelligence to connect to the internet and send me an email or a push notification if the buzzer on the washer goes off
You have essentially described the Protect. Its brain is a cheap little MCU with 128kB RAM. The author, had he read an actual teardown [0], should have realized this. Instead, he made false and confusing claims about Linux.
Certainly other companies put grossly-overspecced hardware in their "Smart" devices, but Nest's Protect isn't one of them.