Aerzeit

Open your window when outside is right.

Aerzeit is a privacy-first iOS app that tells you when to open your windows so outside air becomes inside air at the temperature you chose. Cultural reference: Stoßlüften — the German habit of a short, brisk airing-out — adapted for timing it right, wherever you are.

What it does

Pick the outdoor temperature range you'd be happy to let in. Aerzeit watches the local 48-hour forecast and notifies you whenever conditions match. Turn on the rain filter to skip openings when showers are forecast. Optional filters for humidity, wind, air quality, pollen, and UV let you tune it to what matters to you. No accounts, no tracking; the architecture cannot identify you.

What it doesn't do

Aerzeit doesn't model your room. It tells you when the outside conditions match your target; opening, sizing, and timing the actual airing is yours.

Get the app

Download Aerzeit on the App Store. Requires iOS 16 or later.

The core timing logic will eventually be free on the web, because knowing when to open a window should not require owning an iPhone.