[throwawaynothx]

You can start with a cheap ESP8266 dev board, which I believe is LUA. I made a button that just posts to a backend when we are low on milk in the kitchen for the office at work but you can do some crazy stuff. im sure there are some great books out there but a lot of people just learn by messing around and looking at other peoples tutorials online.

[tomcam]

How do you test for an out of milk condition?

[harry8]

    if(user_has_pressed_out_of_milk_button) {
    ...
    } //??

[watersb]

Tricky. The California Milk Processor Board spent millions of dollars to crowd-source this, and 27 years on, they are still demanding an answer.