The MINOX Suntimer helps estimate the maximum amount of time for safe exposure to sunlight before turning into a prune. The Suntimer is about the size of a watch and is geared towards people who love the outdoors. The device has a sensor that measures the amount of ultraviolet radiation in the sunlight and displays the information on its intensity. The Suntimer audible alarm goes off based on various factors.
From the site:

To determine an optimum time to stay in the sun, important individual factors can be programmed into this tiny instrument, such as skin type and the protection factor of sunscreen in use. In this way, the user gets a maximum time reading which is individually adjusted to his or her personal profile, and when that time expires the Suntimerâ„¢ sounds an alarm to suggest you get out of the sun.

[via Mobile Whack - Gizmologia]