Why Alexa usually won't respond when someone says 'Alexa' on TV

Above: An illustration of how fingerprints are used to match audio. Every incoming audio request to Alexa that starts with a wake word is checked in two ways. It's first compared to a database of known fingerprinted instances of "Alexa," which also make use of the audio that follows the wake word. Then it's checked against a fraction of other requests coming into Alexa devices around the same time. Audio-matching requests from at least two other customers are identified as a "media event" and given increased scrutiny (and potentially declared a match). This contributes to a small cache of fingerprints, allowing Alexa to continue to ignore wake word requests even when they're not happening simultaneously. These fingerprinting methods -- for which Amazon has patents -- will together prevent as many as 80 to 90 percent of devices from responding to TV-originated Alexa statements, the company says.