Various embodiments of systems and methods allow a system to embed an item identifier into a content item. A first device can then play an audio trigger that is imperceptible to humans before playing the item identifier. A second device can go into an active listening mode after detecting the audio trigger and record an audio segment contain the embedded item identifier. A system can then decode the item identifier to determine an appropriate context for the second device. The second device can then receive a vocal command or query and respond according to the determined context. In one example, the first device can be a television, and the second device can be a digital assistant (e.g., Amazon Alexa) that detects advertisements played on the television via audio signals embedded in accompanying audio streams. Subsequent user interactions with the digital assistant can then be informed by the context of the recently-heard advertisements.