Freezidaire

Something's wrong with you refrigerator?
Maybe you can survive by converting your freezer in a refrigerator: here comes the freezidaire!!
The freezer is not meant to be used this way so you can't get e perfect performance but, as I said earlier, you can survive.

The total cost of electronic hardware can fall within ten dollars (december 2015), you can complete it with some wire and plugs staying within 20 bucks.
The real cost in this IoT era is software, it takes me a dozen hour from inception to production, being the first project of this stream, next ones required smaller developement efforts.

I've found NodeMCU firmware really bootstrapping for these project, lua learning curve wasn't a problem and many examples are available.
ESPlorer is a great tool and www.esp8266.com provides a really supporting community.
My ESP8266 was a ESP-07 module with 512KB and the lua approach let me with very few available memory: the solution is to buy a recent SoC with at least 4MB or use a custom build of NodeMCU with only your needed modules.

Thingspeak is amazing, the log and the visualization features you can see in this page are awesome, so are the ThingTweet (the Freezidaire had more followers than me), the react, etc.
A special mention is that for the Talkback, I was able to add a remote controlled temperature setpoint with minimal effort.

Let's review the whole thing:
- The Freezidaire has complete logs, it is easy to build some analytics on them in TS
- It has an advanced diagnostic: you get notification if temperature falls outside the safe range (e.g. door left open), you get notification if it can't connect to TS for a while, you get a "Everything's OK" tweet at the end of each zero-issue-day
- It allows you to change it's temperature (setpoint) remotely

Any of the lessons I've learned with the Freezidaire is part of the foundation of each next IoT project I've started and ESP8266 and ThingSpeak are the heart of it.