Use this in combination with "If it's nice outside during the summer then send a notification to open a window" to turn off the A/C and remind you to open a window when it is cool enough outside
If
Thermostat outdoor temperature is less than
This trigger fires every time your ecobee thermostat senses that the outdoor temperature is less than a specific value you supply.
Then
Send a notification from the IFTTT app
This action will send a notification to your devices from the IFTTT app.
Discover more time saving integrations for Notifications and ecobee