1. A method for generating a gesture-detection (GD) filter comprising: receiving sensor data captured by at least one sensor during a gesture, the at least one sensor selected from the group consisting of (i) a motion sensor that is attached to a user, (ii) a motion sensor that is attached to a user equipment, (iii) an audio sensor, and (iv) an electrode array attached to a head of the user, the sensor data comprising a plurality of sequential sensor measurements; determining a set of activity frequencies associated with the sensor data received during the gesture; iteratively calculating: (i) a prediction error based on a difference between at least one of the plurality of sequential sensor measurements and an observation prediction ĥ t from an observation model, the observation model operating on phases in a set of phases associated with the set of activity frequencies; (ii) an updated set of estimated activity phases based on the prediction error and the set of activity frequencies; (iii) an updated observation function of the observation model based on the prediction error; and generating the GD filter based at least in part of the set of activity frequencies and the updated observation function.