The bottle is thirty millilitres of amber glass with a black cap. It has no battery. It does not sync. It has never asked for an update, and it will not stop working when a company loses interest in it.
It sits on the edge of the bath and does one thing. That is the whole design.
An object that cannot ask for anything
Almost nothing else in the room is like this. The tap is fine. The towel is fine. Everything else you own that cost forty dollars has firmware.
Amber glass is not styling. Essential oils degrade in light, so the glass is dark for the same reason a dispensary bottle is dark — it is a functional decision that happens to look like a decision. The cap is black because a black cap does not draw attention to itself on a wet ledge.
Ten drops into running water. Twenty minutes. Door closed.
Thirty millilitres
At ten drops a bath, a bottle is roughly sixty baths. That is a year of Sundays, or a hard month.
When it is empty you will know, because the weight changes before the level does. Then you buy another one, or you do not, and nothing sends you a reminder either way.