Going outside and soaking up some sun and warm weather is a joy, but remembering to reapply sunscreen can be a pain. It's still necessary though, and Adafruit's Becky Stern has an ingenious solution you can wear on a hat or other piece of clothing that watches your exposure and reminds you to reapply regularly.
You may remember Becky Stern from her How I Work feature here at Lifehacker, or the last few projects of hers that we highlighted. Her video above is a good walkthrough of the device -- you'll need an Adafruit FLORA wearable microcontroller and a UV index sensor, but not much else. Conductive thread to tie everything together, and the project is pretty simple.
The UV index sensor will keep an eye on your exposure, and the Flora will process the data and sound the alarm when it's time for you to get out of the water or head back to your bag to reapply your sunscreen. That way you can have fun without wondering how long it's been since you put some on. The whole thing is simple enough to do in an afternoon, and the resulting sensor isn't so obtrusive that it looks ridiculous on a hat -- we imagine if you're worried about it, there are other ways to conceal it as well, or even protect it a bit with cellophane tape so it's water resistant. Hit the link below for the full project.
Sunscreen Reminder Hat [Adafruit Learning System]