1. An apparatus comprising; a speaker; a microphone to generate one or more audio signals from sound captured within an environment; a processor; and computer-readable media storing computer-executable instructions that, when executed on the processor, cause the processor to perform acts comprising: identifying, based at least in part on the one or more audio signals, a request from a user to initiate a transaction; outputting, via the speaker, a request that the user utter a password associated with the user; determining, from the one or more audio signals, whether a first utterance of the user includes a password that matches the password associated with the user and whether an audio signature of the first utterance has a similarity score to an audio signature associated with the user that is greater than a first pre-defined threshold, the audio signature of the first utterance being based at least partly on a pitch, a decibel level, and a tone associated with the one or more audio signals; at least partly in response to determining that the passwords match and that the similarity score of the audio signature of the first utterance to the audio signature associated with the user is greater than the first pre-defined threshold, causing output of, via the speaker, a request that the user answer a pre-stored question having a previously selected answer; determining, from the one or more audio signals, whether a second utterance of the user includes the previously selected answer and whether an audio signature of the second utterance has a similarity score to the audio signature associated with the user that is greater than a second pre-defined threshold; and initiating the transaction at least partly in response to determining that the second utterance includes the previously selected answer and that the similarity score of the audio signature of the second utterance to the audio signature associated with the user is greater than the second pre-defined threshold.