How can I get automatic notifications that the outside temperature (in Sydney CBD) is below a certain threshold, and therefore the best option is to turn off the air conditioning and instead open the windows?
The automatic notification should ideally be via Slack, but email is also fine. Nothing that requires a mobile phone, such as SMS alerts or a smartphone app. The service should be either free or very low cost.
Buying air conditioners that are intelligent about the external temperature is presumably impractical, as the air conditioners have already been purchased, as would changing the architecture of the building. (And please don't suggest we use fans - we're currently using a mixture of fans and aircon)
On r/frugal, a similar question was asked. The only worthwhile solution was using ifttt.com, but without any mention of specific "if" or "do" recipes.