A classifier for classifying sensor samples in a sensor system, the sensor system comprising N force sensors each configured to output a sensor signal, where N>1, each sensor sample comprising N sample values from the N sensor signals, respectively, defining a sample vector in N-dimensional vector space, the classifier having access to a target definition corresponding to a target event, the target definition defining a bounded target region of X-dimensional vector space, where X≤N, the classifier configured, for a candidate sensor sample, to perform a classification operation comprising: determining a candidate location in the X-dimensional vector space defined by a candidate vector corresponding to the candidate sensor sample, the candidate vector being the sample vector for the candidate sensor sample or a vector derived therefrom; and generating a classification result for the candidate sensor sample based on the candidate location, the classification result labelling the candidate sensor sample as indicative of the target event if the candidate location is within the target region.