Lüften

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.