Alert settings are found on the Meter settings page in the App.
To access the Meter settings, tap the gear icon in the upper-right corner of the Meter you want to control in the SwitchBot App homepage. Then click "Desired Conditions".
You'll see two sliders, one for temperature and one for humidity. Each slider has two handles. By default, the blue area between these two handles is the desired range of conditions.
If the "Alert Me" toggle is enabled, you'll be notified whenever conditions leave this zone.
If the "Inverse" toggle is enabled, the blue area is either in between the two handles or outside the range.
Alerts are sent using notifications, which is the same technology news companies employ to send out breaking news alerts.