1. One or more computing devices comprising: one or more processors; and one or more computer-readable media storing computer-executable instructions that, when executed by the one or more processors, cause the one or more processors to perform acts comprising: receiving a first voice command requesting performance of a first operation, the first voice command being associated with a first voice signature; causing performance of the first operation at least partly in response to receiving the first voice command; receiving a second voice command requesting performance of a second operation, the second voice command being associated with a second voice signature; calculating a similarity between the first voice signature and the second voice signature; determining, based at least in part on the calculated similarity, whether to: (i) cause performance of the second operation, or (ii) refrain from causing performance of the second operation.