The man who co-created Apple's virtual assistant Siri found the 2013 science fiction film Her a challenge.
Given it stars an artificial intelligence named Samantha, it is a little like going to the office.
Adam Cheyer, who has worked on digital assistants for almost 25 years, could not turn off what he calls his "engineering mind".
He deconstructed the technical process behind each word Samantha said until the moment the film's hero Theodore goes to bed and she asks: "Can I watch you sleep?"
"There's no informational content that can be derived from observing a prone human," Mr Cheyer laughs.
"The only explanation can be emotional love. I don't know how to do that. And I threw up my hands."
Mr Cheyer may not be able to engineer emotional love into virtual assistants (yet), but he has played a vital role in bringing the chatty technology to our smartphones.
Shortly after his team offered an early version of Siri on the App Store in 2010, Steve Jobs called, and the product launched on the iPhone in 2011.
Mr Cheyer no longer works for Apple, instead working on his own artificial intelligence company Viv Labs, which was bought by Samsung last year.
These days, a new industry of home assistants is popularising the conversational interface. They play music on command, read the news and deliver weather reports.
Almost half of US adults use voice assistants to interact with their personal devices, but Mr Cheyer doesn't think the technology is quite ready for primetime.
The rise of voice
Adam Cheyer thinks voice is going to be based on trust, even more than the web
Photo by Sergii Kharchenko/NurPhoto via Getty Images
When he first built a version of Siri, Mr Cheyer had never seen a web browser. Even today, the virtual assistants on the market are far from the vision of usefulness he formed in the early 1990s.
They still perform only a narrow set of functions: send texts, check stocks, call your mum.
"People use, in small ways, voice assistants and other assistants every day … but they're still not very important," Mr Cheyer says.
He wants the virtual assistant to become your primary means of interacting with computers and information — an "ubiquitous interface" — the same way you might use a smartphone or web browser today.
To get there, Mr Cheyer believes the assistant needs to become untethered from a single brand or device.
"Today an assistant is a feature that sells devices," he says. "The only phone you can get Siri on is an Apple phone. The same with Google."
Instead, he wants you to interact with just one assistant throughout your day, whether in the car, at work or watching TV.
He also wants the virtual assistant to be personalised.
"Today, Siri, Cortana and the others are exactly the same assistant for every user," he explains.
"I want an assistant that can do the things I want it to do … my hobbies, the brands I care about, the services I access. My assistant should know about that."
Can you trust the disembodied voice?
Unlike using online search the old-fashioned way — with your typing fingers — voice interaction feels far more intimate.
This is intentional: the informal tone and cheery personality nudges you towards an emotional attachment.
When creating Siri, Mr Cheyer and his team knew it had to be somehow embodied.
They answered questions like: is Siri a man or a woman or neither? Is it human or a machine or neither? Is it an employee of Apple or a fanboy of Apple or neither?
But if something speaks, it must also listen.
Our phones are always near us and our home assistants sit there, squat on our kitchen bench, eternally listening for the word that will wake them up: "OK Google" or "Alexa".
This has already raised privacy concerns. The American Civil Liberties Union, for one, has weighed in:
"Digital assistants and other IoT devices create a triple threat to privacy: from government, corporations, and hackers," it warns.
In Mr Cheyer's view, assistants are built on the same technology as the internet, smartphone and apps. You must decide what of yourself you're willing to share.
"It's going to be based on trust, even more than the web," he says.
Is voice just another way to serve ads?
This trust relationship also makes monetising the virtual assistant difficult.
If you share your most sensitive queries and plans with this voice, it would be jarring to hear it suggest you try a food home delivery service you have no use for.
Notifications and interjections from talking devices could steal even more of our attention.
Mr Cheyer says developers must act delicately because of this dynamic, although he does think there will be a way to serve sponsored results.
But what if one of the big voice assistant brands breaks this trust covenant, either by serving intrusive ads or worse?
In an age when information warfare is served on your Facebook newsfeed, this doesn't feel unlikely.
"If one violated this trust in some way, does that bring down the whole industry? Perhaps," he ruminates.
Of course, being the so-called father of Siri means Mr Cheyer is bullish on the future of voice.
His home is filled with voice assistants, but will one become the emotional crutch that Samantha was for Theodore?
Mr Cheyer thinks not.
"I want humans to be my emotional relationships, absolutely," he said.
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