A mobile fall arrester for rope descents with locking function. Working in a comparable way to a seat belt in a car, the device allows the user to work and move freely in normal at height work situations, but when there is a sudden movement, such as the user falls or slips, the fall arrester locks on the rope and the user stops immediately. Has an integrated locking function that enables the user to immobilize the device to reduce the potential fall distance. Used with either the Petzl ASAP'SORBER Energy Absorber or Petzl ASAP'SORBER AXESS Energy Absorber (for loads of up to 250 kg in two-person rescue situations), so that the user can work at a distance from the rope.