Smartphone and speaker voice assistants can be hacked using lasers

As keen tech adopters know, Google Assistant, Amazon Alexa, Apple Siri, and Facebook Portal are AI-powered internet platforms that users control by issuing voice commands through smartphones or home ‘smart’ speakers.

Or at least that’s what we thought until this week when a US-Japanese team published a research paper which confirms an interesting and under-estimated possibility – these devices will also accept “signal injection” commands sent to them using pulses of laser light over distances of a hundred metres or more.

Hitherto, hacking such systems has been about sending them audible commands without their owner’s knowledge. Now the research confirms that it’s possible to achieve the same result over considerable distances in ways that might allow attackers to unlock “smartlock-protected front doors, open garage doors, shop on e-commerce websites at the target’s expense, or even locate, unlock and start various vehicles” that are connected to the victim’s Google account.

It’s a point worth remembering – voice assistants aren’t just gimmicks or conveniences and a growing volume of security-sensitive technology is now hooked up to them.

The shining

But voice-controlled devices accepting commands by way of light?

It sounds unlikely but what makes it possible is the photo-acoustic effect which has been around since 1880 when the scientist Alexander Graham Bell invented an optical communication device exploiting it.

He discovered that shining light on to an object causes it to heat up very slightly in a way that generates sound waves, which microphones, including today’s MEMS (micro-electromechanical systems) diaphragms, turn into electrical signals.

The researchers summarise this:

Thus, by modulating an electrical signal in the intensity of a light beam, attackers can trick microphones into producing electrical signals as if they are receiving genuine audio.

Engineers, including those designing voice-controlled devices, should know this. Unfortunately, Graham Bell’s discovery lost out to radio communications, and photo-acoustics were sent to the back burner.

The principle is explained in a video made by the researchers.


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