I live in the Bay Area, and so the weather cools down to a comfy temperature in the evenings. Opening up the windows to let the fresh air in has saved me a decent amount on A/C bills. Checking a forecast every hour to catch that moment is exactly the kind of job a computer should do.
PorchWeather watches one saved location and a set of conditions you pick (temperature range, wind, rain, dew point, air quality) and sends you a notification when conditions become nice, and another when they stop. That's the whole product. It's free, web-native (not an app), and notifications are browser push or email.
Some implementation details HN might find interesting:
Stack: SvelteKit SPA, Rust backend, DynamoDB, Cognito for auth, SES for email, Self-hosted Open-Meteo for weather all on ECS Fargate. The weather layer serves ECMWF global plus NOAA HRRR at 3 km resolution for the US.
Notifications are primarily through web push. I'd love to do SMS through twilio, but it seems prohibitively expensive for a free service unfortunately. iOS devices make this a little harder because you have to "install" the app on the home screen to get push notifications. I may end up creating an app at some point to make this easier if there's demand.
I do think this is an interesting concept. Would API integration endpoints that users could configure directly to poll your service with their home automation assistants get past the need to be notified? If they could poll at their own pace, the could alleviate the uncontrolled cost.