The devices monitor distance, the amount of hard braking and acceleration, and the time of day. Driving at low risk times of the day and avoiding being on the road between midnight and 5 a.m. is rewarded. The device doesn’t differentiate between drivers, so it is the record of everyone who gets behind the wheel of a vehicle that determines the discount.
http://www.windsorstar.com/business/discount+driving+safely/9029631/story.html