Petzl's PET-B71 ASAP Mobile Fall Arrester
Sounds like the Petzl's PET-B71 ASAP Mobile Fall Arrester. This device works on the same concept as a seatbelt in your car if you pull slowly it lets out pull fast and the seatbelt locks. I have one it is very simple to use and as long as you use one of the many diameter ropes it is desined for (I use 7/16" static) and rig it right you cant mess it up just set it and forget it. It can be used in rappelling or climbing. It has a very slight drag as you rappel just enough to keep the device trailing above you. If useing it as a self belay for climbing it has no drag and freely trails you up the rope. If you go to fast or fall and it locks you have to use a prusik knot step or other methed to get your weight off of it and turn the wheel backwards this unlocks it. When it locks with full weight on it it causes little to no damage to rope. I dont always use it as somethimes I like to rappel faster than it will alow (speed set not adjustable) but if I dont use it I always use a prusik knot as a self belay either above my rescue 8 or just below my brake hand cliped into the leg strap (newer way). This piece of gear is completly mechanical. price is around $200 differs a few bucks on diffrent web sites. Stay safe and have fun.
The "clipup" is not sold as a fall arrester and if you are unconscious the device will not lock and does not sence speed. Still a cool peice of gear though.