My doorbell is a sign that says "Knock", because my 70's doorbell is broken. It requires 0 cloud services to fix the problem of people pressing an unhelpful button.

[EDIT] To people downvoting this, did you read the article? Specifically, this part:

"Before we had the doorbell, people just knocked on the front door. But now, people would notice the doorbell and ring it instead. This would send a notification to our phones, and then it would also helpfully play a sound on the doorbell itself… outside the door… which we could not hear."

He then goes on a tech bodgeathon to fix the button, instead of just placing a sing that says "Knock" to go back to the thing that worked before.