I've been thinking about this project for a while now (been bitten by leaving my insulin in the car a few times when I thought a few minutes wouldn't be enough to affect it, or simply having forgotten it).

This is actually my second go at this. My previous plan was to use a NeoPixel ring as an indicator, with an ATtiny85 as the brains. Had it prototyped but found it just did't relay quite all the information I wanted (max temperature, min temperature, times, battery, etc.) clearly enough. Also, trying to debug code on the ATtiny was a bit painful.

My new approach is based around one of the small 128x32 OLED displays from Adafruit. This has a few advantages; I can display much more detailed information, plus the rectangular shape fits nicely with the Trinket and the LiPo battery I've got in mind. Throw in a 3D printed case and it should end up being quite a neat little unit.