https://techcrunch.com/2019/01/31/heres-why-amazons-super-bowl-ad-wont-trigger-alexa/

South Park famously annoyed the world by triggering Echo and Google Home devices with familiar wake words. When Amazon’s at the wheel, however, the company is able to ensure that Alexa stays quiet using a method called acoustic fingerprinting.

In the lead up to the Super Bowl, the company’s offered a (relatively) easy-to-understand breakdown of why its celebrity-laden ads won’t wake up Alexa during the big game. With its own ads, the company adds a fingerprint of the audio, which is stored on-device.