1. A method comprising: receiving, by an electrode of a device, a signal from a body of a user, the signal based on an electromagnetic interference signal generated by an object that is external to the device; determining, by a computing device, one or more of the following based on machine learning applied to the received signal: an identity of the object; an interaction between the user and the object; or a context surrounding the device; and optimizing, based on the received signal, a classification model identifying a plurality of fingerprints, wherein optimizing the classification model comprises: identifying a fingerprint corresponding to the received signal; presenting to the user an identification of the fingerprint corresponding to the received signal; receiving, from the user, input identifying whether the fingerprint corresponds to the received signal; and updating the classification model based on the input.