If you scroll down to the tech specs, you'll see a list of sensors onboard the device:
Optical heart rate sensor
3-axis accelerometer/gyro
Gyrometer
GPS
Ambient light sensor
Skin temperature sensor
UV sensor
Capacitive sensor
Galvanic skin response
Microphone
Perhaps my use of the phrase "real time" was an embellishment/exaggeration (you'll forgive my enthusiasm, I hope)... it's not clear if the device produces a continuous (is that the right word?) measure of the UV index, or if you have to invoke the sensor manually when you want a reading.
Edited by blood, 30 October 2014 - 09:13 AM.