We deleted the on switch

There is no on and there is no off. Press it and it wakes; finish and it sleeps.

This is not about saving a button. The concept of a power switch exists because devices burn too much power on standby, so the user has to take responsibility for switching them off. If standby is cheap enough, there is no reason for that burden to exist.

100 microamps

In deep sleep the whole device draws about 100 microamps. At fifteen minutes of recording a day that works out to roughly 18mAh, so a 300mAh battery runs for over a month on one charge.

At that order of magnitude, "I forgot to switch it off" stops being a mistake with consequences. So we deleted the mistake from the product rather than adding a button for you to avoid it with.

The moment you press it

Waking from deep sleep takes time, and people start talking the instant they press. So once the button wakes the chip there is a short pre-roll buffer behind it: the audio from just before the press is in there too.

You do not lose the first word. You will never notice this, because it is the kind of thing that is only noticed when it has not been done.

Recording never touches Bluetooth

This is our favourite part of the design.

The button wakes the chip and the audio is written straight to local flash. Bluetooth only wakes up afterwards to sync, then disconnects immediately and goes back to deep sleep.

Three consequences: it records perfectly well with the phone nowhere nearby; a failed sync loses nothing, because that recording was never on the radio to begin with; and the power cost of recording is a storage write with no radio attached — which is where the month of battery life actually comes from.

What happens when the battery dies

The firmware seals the current file before the battery bottoms out, so whatever has already been recorded is intact. With the five-minute segments on top of that, the worst case is losing under five minutes at the end.