The DolphinAttack technique allows hackers to control Siri, Google Now, Alexa and other voice assistants with commands in ultrasonic frequencies. The researchers were able to modulate various voice commands on ultrasonic carriers making them inaudible to humans. The attack technique was dubbed DolphinAttack, it was successfully tested against Amazon Alexa, Apple Siri, Huawei HiVoice, Microsoft Cortana, Samsung S Voice, and also the speech recognition system installed an Audi Q3 models. The team tested the DolphinAttack method against 7 different speech recognition systems running on 16 devices.”]
Source: https://securityaffairs.co/wordpress/62838/hacking/dolphinattack-ultrasound-mobile.html