Breadwinner "Wi-Fi connected Growth Sensor screws onto the top of any wide mouth (86mm) mason jar. It measures the (Sourdough) Starter’s rate of rise after a feeding and until it peaks a few hours later, marking its readiness to use"

https://www.engadget.com/three-kitchen-gadgets-to-take-the-guesswork-out-of-sourdough-164536914.html