As a technologist who builds products, few things have excited me more in my career than the evolution of voice technology. More than just a way to replace manual inputs, voice represents a profound shift in how we interact with products, and how we expect them to interact with us.

Voice functionality is at its best when the technologists who build it embrace the full experience, so I thought I’d share four key principles on voice control.

• Voice is communal and not personal. It democratizes control: anyone who has access to / or is in the proximity of your always-on device (including inanimate objects like TVs/radios) can trigger actions. As adoption grows, so goes the exposure. Already we’re seeing incidents of ambient sounds, like TV shows triggering smart home devices, and that trend will accelerate unless we address it.
• Voice interfaces are at their best when they incorporate sight and touch: Say you initiate a voice search on a topic and the response to that search has more than 5-6 options. It is better if the results are displayed spatially on a screen (TV/mobile/Tablet) rather than narrated serially via a speaker. You can then use a tactile interface to choose the options.
• Voice is inhibited by social norms: I don’t know about you, but screaming a guard word followed by commands when you have company/in front of guests can be a tad awkward/out of norm. We need to build voice interfaces that are not only functional, but also fit into our real lives. 
• The best approach puts voice “control” in the hands (or mouth) of the user: As we design voice interfaces, giving the user a sense of control and imbuing trust will go a long way in driving engagement. Having a push-to-talk option makes users more comfortable with voice technology, as does the ability to easily shut it off.

We are entering a new era of interfaces, moving from the world of mobile where the rules of interface design are well known, to a world of ambient interfaces (era of IoT and Machine Intelligence) where technology is looking to adapt to us. These rules are not yet written. Product developers need to carefully understand the different modes (voice/visual/touch), channels (Mobile, web, TV, speakers) and the overarching context as interfaces are designed. In addition to this, trust plays a big role in always-on devices like ambient microphone and cameras… After all, the last thing I want to be paranoid about is my camera measuring my waistline, while I see advertisements about diets on my phone.