Arduino Controlled Fire/Temp Sensor and Mains Power Down


I have a 3d printer which I in the event of it getting to hot, I want to be able cut the mains power to. I have built a cabinet for it and that has it’s mains power controlled by a smart plug. Using ITTT I have set it up a web hook, that will notify my mobile phone and cut the power to the printer. This works fine when it’s webpage is loaded.

What I would like advice on is how I should set up the Arduino end. I have set up an Uno with an ethernet shield and a tmp36 temperature sensor and used a sketch that displays the temperature was a web server in the past.

Can anybody advise me how I can use a sketch that will call a webpage up if the temperature goes above a pre-defined value?

I also would like to connect a smoke alarm to the arduino so that if it was triggered the Arduino would load the same webpage, cutting the mains power and notify me.

Many thanks in advance.