Lights

http://www.exposurelights.com/product/000086/reflex-mk1-(new)/

Bastards release funky new one after I shell out for their flagship model. How dare they?!

#whatthefuckisreflex

When climbing Reflex gradually eases off the power preserving battery life for when it is needed most. As soon as the light senses acceleration or that it is heading down hill, Reflex quickly brightens to give the maximum output.

They seem to assume that you go fast downhill and therefore need more light then. Sounds like there's a pitch sensor & accelerometer in the light, linked to the brightness.