Voice recognition systems can be activated without saying a word by sending commands at very high frequencies (ultrasound). It is because of the ability of micr

Voice recognition systems can be activated without saying a word by sending commands at very high frequencies (ultrasound). It is because of the ability of microphones to detect these frequencies. This could be used for jokes when an assistant like Alexa will say something while nobody has heard anything. Or by hackers, for example, to unlock a phone. https://techcrunch.com/2017/09/06/hackers-send-silent-commands-to-speech-recognition-systems-with-ultrasound/ https://techcrunch.com/2017/09/06/hackers-send-silent-comman...