1. A system comprising: one or more data processors; and a storage device storing instructions that, when executed by the one or more data processors, cause the one or more data processors to perform operations comprising: accessing a set of historical response data associated with a set of content items and a set of historical sensor data associated with the set of historical response data, generating a predictive model for the set of content items based, at least in part, on the set of historical response data and the set of historical sensor data, wherein the predictive model outputs a value for a content item of the set of content items in response to receiving a set of sensor data from a mobile device, wherein the received set of sensor data from the mobile device is combined with a content item request in a URL string, selecting a content item based, at least in part, on an output of the predictive model in response to receiving a set of sensor data from a mobile device, and outputting data to effect presentation of the selected content item.