In 2009, I could send and receive text messages though SMS gateways that would control my arduino-controlled hot tub that my friends and I got for $100 on Craigslist. I could adjust the temperature and it would acknowledge and tell me when the programmed temperature would be reached based on the time derivative. This was useful as a grad student in Ann Arbor winters.<p>I had a python script running on a handmedown computer running Ubuntu 8.10 that just periodically checked an email account, parsed the command, flipped the relay as necessary, read the temperature rise, and replied.<p>Writeup: <a href="https://partofthething.com/thoughts/hot-tub-controller/" rel="nofollow">https://partofthething.com/thoughts/hot-tub-controller/</a>