The best wearable is the one you were already wearing

The graveyard of wearable computing is full of well-made objects that failed the same test. Not the technology test — the pocket test. Something new has to be picked up, remembered, charged, explained, and defended, every single day, before it delivers any value at all. Most people run that calculation once, decide it is a lot, and the device ends up in a drawer with the fitness tracker.

There is a shortcut, and it is not a technical one. Build on an object the person already wears for another reason.

What sunglasses already have

Sunglasses solve a real problem that has nothing to do with us: the sun is bright and eyes are sensitive. That means the wearing decision is already made, for reasons that would hold if we did not exist. Nobody has to be convinced to put them on, because the sun is doing the convincing.

They also happen to sit in the single best position on a human body for a microphone that wants to hear one person and nobody else: fixed relative to the mouth, a handful of centimetres away, with a rigid structure to hold two microphones a known distance apart. If you were designing a mount for near-field voice capture from scratch, you would arrive at something remarkably like a spectacle frame.

The device is not competing for space on your face. It is already there, and we added one thing.

And they subtract. If you wear these outdoors, you are not also carrying earbuds. That is one object fewer to lose, charge, and find. Very few products in this category can honestly claim to reduce the count of things in your pockets.

Prescription changes the arithmetic completely

Sunglasses get worn when the sun is out. Prescription glasses get worn every waking hour, without a decision, because the alternative is not seeing.

That difference is roughly a factor of ten in wearing time, and it converts the product from something you remember to bring into something that is simply on your face when a thought arrives. It is why prescription is offered at all — not as a margin exercise but because it is the difference between a gadget and a tool.

What the constraint forces you to remove

Building on an object people already wear imposes a discipline that turns out to be the most valuable thing about it. Anything that would make the object worse in its original job has to go.

• A camera makes sunglasses socially expensive. It changes every room you walk into, and no amount of design language fixes that. Out.
• A display makes sunglasses heavy, hot, and short-lived. Out.
• An indicator light makes sunglasses irritating to wear and, in the evening, actively bad for you. Out.
• A wake word makes sunglasses into a thing that is always listening, which makes them a thing people take off. Out.
• An on switch makes sunglasses into equipment. Out.

What survives is a headset, one button, and sixteen hours of storage. It reads as a minimal product and it is really the residue of a constraint: everything else broke the object we were building on.

The thing it is actually for

The reason to want any of this is narrower than the category suggests. It is the four seconds between having a thought and having somewhere to put it — the interval in which you reach for a phone, unlock it, find an app, and discover the thought has changed shape or gone.

Ideas do not arrive at desks. They arrive while walking, running, waiting, pushing a stroller, on the third kilometre when you have stopped thinking about your feet. All of those are outdoors, and all of them are places you were wearing sunglasses anyway.

Press once, say the thing, keep walking. That is the entire product. Everything above is what it took to make those three steps not require thinking about.