The patent broadly describes two techniques. The first calls for transmitting a snippet of a commercial to Echo devices before it airs. Then the Echo can compare live commands to the acoustic fingerprint of the snippet to determine whether the commands are authentic. The second tactic describes how a commercial itself could transmit an inaudible acoustic signal to tell Alexa to ignore its wake word.
About a year ago, a Reddit user calling himself Asphyhackr did a little more legwork and concluded that Amazon was creatively employing this second technique.
Will be amusing — insofar as silly patent fights are ever truly amusing — if Amazon tries to keep Apple and Google from doing the same thing in commercials.