A decentralized relaying algorithm for mobile devices is described. The coupler includes a conductive portion movable by an adjustable member from a non-conducting retracted position spaced apart from the power transmission line to a forward conducting position in electrical contact with the power line. File data and metadata may be secured with encryption andor authentication mechanisms. To solve the problem, the invention essentially proposes to provide a protection device, which effectively protects the personnel operating the fire-fighting trailer and also guarantees the possibility of rescuing persons from the scene of a fire. It is controlled to divide the printed sheets into sheets at the sheet count received from the user and stack the printed sheets on the sheet stacking unit. It is further provided a multi-mode remote controller, a user terminal and a system.