Abstract: In general, a system can include an interface component configured to receive measurement data from a motion sensor unit physically coupled with a movable part of a body of a user. The measurement data can include sensor data of a sensor of the motion sensor unit that corresponds to a second derivation in time of a trajectory of the motion sensor unit. A data storage component can store technical profiles associated with characters and can include at least a plurality of predefined acceleration profiles. Each acceleration profile can include acceleration data characterizing a movement associated with a specific portion of a potential trajectory of the motion sensor unit in the context of at least a previous or subsequent portion of the potential trajectory. A decoding component can compare the received sensor data with the plurality of predefined acceleration profiles to identify a sequence of portions of the trajectory.