1. A system comprising: one or more processors; and one or more computer-readable media storing computer-executable instructions that, when executed on the one or more processors, cause the one or more processors to perform acts comprising: receiving, during a first time period, first sensor data from a first sensor within an environment indicating that a door within the environment has been opened; receiving, during the first time period, second sensor data from a second sensor within the environment indicating that motion has been detected within the environment; receiving, during the first time period, an indication that a first device within the environment has been powered on; receiving, from a second device within the environment, an audio signal representing speech of a user, the speech including an indication that the user has arrived at the environment; performing speech recognition on the audio signal to identify the speech; identifying a model previously associated with the indication that the user has arrived at the environment, the model based at least in part on sensor data previously received from the environment; inputting the first sensor data, the second sensor data, and the indication that the first device has been powered on into one or more machine-learning algorithms to train the model; receiving, during a second time period, third sensor data from the first sensor indicating that the door within the environment has been opened; receiving, during the second time period, fourth sensor data from the second sensor within the environment indicating that motion has been detected within the environment; determining that the third sensor data and the fourth sensor data correspond to a class specified by the model; and sending an instruction to power on the first device within the environment at least partly in response to determining that the third sensor data and the fourth sensor data correspond to the class.