Lüften

Two notifications a day, zero guesswork. Lüften tells you exactly when to open your windows — and when to close them before the heat returns.

Open your windows at the right moment. Close them before the heat gets back in.

Lüften watches tonight's forecast and tells you the two moments that matter: when outside has cooled enough to bring fresh air in, and when it's about to warm up again. That's it.

WHY IT WORKS Passive cooling — moving cool night air through your home — is one of the most effective ways to keep a house comfortable without air conditioning. The problem is timing: open too early and you let warm air in; wait too long and you miss the cool window. Lüften solves the timing problem.

WHAT YOU GET • An alert when outside drops cool enough to open your windows • An alert before the heat returns in the morning • A forecast view showing your opening window for tonight • No indoor sensors, no smart home, no account

HOW IT WORKS Set your location once. Lüften fetches your local weather forecast and works out the best window-opening window for tonight. At most two notifications a day — one to open, one to close.

PRIVACY FIRST No account. No sign-in. Everything stays on your device. Your location is used only to fetch the local forecast and is never shared.