Ultrasonic waves do not make a sound, but they can still activate Siri on your cellphone and have it make calls, take images or read the contents of a text to a stranger — without the phone owner’s knowledge, suggests a new research. Researchers have previously shown that ultrasonic waves can be used to deliver a single command through the air. However, the new research from Washington University in St Louis expands the scope of vulnerability that ultrasonic waves pose to cellphone security.
These waves, the researchers found, can propagate through many solid surfaces to activate voice recognition systems and — with the addition of some cheap hardware — the person initiating the attack can also hear the phone’s response. The results were presented at the Network and Distributed System Security Symposium in San Diego. “We want to raise awareness of such a threat,” said Ning Zhang, Assistant Professor of at the McKelvey School of Engineering. “I want everybody in the public to know this.” Zhang and his co-authors were able to send “voice” commands to cellphones as they sat inconspicuously on a table, next to the owner.
With the addition of a stealthily placed microphone, the researchers were able to communicate back and forth with the phone, ultimately controlling it from afar. Ultrasonic waves are sound waves in a frequency that is higher than humans can hear. Cellphone microphones, however, can and do record these higher frequencies. “If you know how to play with the signals, you can get the phone such that when it interprets the incoming sound waves, it will think that you are saying a command,” Zhang said.