something that will come in handy for the summer and the beach!

from their website:

Sundiwear™ shows your risk of skin damage and sunburn from harmful ultraviolet rays.

Sundiwear™ stickers change color to show you when it's time to reapply sunscreen!

Application – and timely reapplication – of a sunscreen with an SPF rating of 15 or higher is an important step in helping to avoid the dangers of sunburn and sun-related skin damage. Sundiwear™ stickers take the guesswork out of knowing when it is time to reapply your sunscreen by changing color in response to the sun's harmful UVA and UVB rays according to actual climate conditions.

here is the link for a free pack of stickers:
Sundiwear™ stickers