Privacy is a placement problem

Every wearable microphone eventually has the same conversation. Someone asks whether it records the people nearby, and the company answers with a policy: we do not store it, we do not train on it, you can delete it, there is a light. All of those are promises. All of them can be changed by an update, a new owner, a subpoena, or a bug.

We wanted an answer that is not a promise.

Two microphones and a subtraction

There are two microphones on Razzhood Glasses and they are not a stereo pair. They are a comparison.

• The main mic is at the bottom centre of the left rim, port facing down at your mouth, 4 to 7 centimetres away.
• The reference mic is at the top corner of the right rim, port facing up and tilted 15 to 20 degrees back — away from your mouth, with the frame body between it and your face. About 12 centimetres.

When you speak, the distance ratio alone gives the main mic about 5.3 dB more level, and the port orientation and the shadow of the frame add another 2 to 4. Total: 7 to 9 dB.

When somebody else speaks from half a metre away, they are almost exactly the same distance from both microphones. The difference collapses to under 1 dB.

Set the threshold at 4 to 5 dB. Above it, write. Below it, do not. That is the entire privacy architecture, and it is a subtraction and a comparison — no DSP, no beamforming, no voiceprint, no model, no inference, no cost, and nothing running in the background listening to decide.

Why physical is different from good

A threshold is firmware, and firmware can be updated. But a firmware update cannot move a microphone to the other corner of a frame and turn it to face the sky. The guarantee is not that we will behave; it is that the arrangement of holes in a piece of nylon makes the other outcome physically hard, and would keep making it hard if we were replaced tomorrow by people with worse intentions.

The best privacy feature is the one that survives the company changing its mind.

This is also why there is no setting called "record everyone". Not because we hid it — because there is nothing to expose. You cannot toggle geometry.

What this design gives up

It gives up a real capability, and we should say so plainly. These glasses are bad at recording a meeting, an interview, a lecture, or a conversation with your grandmother. If that is your job, buy a dedicated recorder, and it will cost less than this does.

What we get in exchange is a device that is boring to everyone but the wearer. Nobody in the room needs to negotiate with it. There is nothing to be told about, nothing to consent to, and nothing pointed at anybody. The social cost of the product is close to zero, which is the property that decides whether a wearable is worn.

And why it removed the light

Once the microphone cannot pick up bystanders, a recording indicator has nothing left to indicate. That is worth noticing, because the light is normally treated as the ethical minimum — the thing a responsible company adds. It is more accurate to see it as compensation for a design that needed compensating.

We would rather remove the cause than add the warning. The light has its own set of problems, and none of them had to be solved once this one was.