When you're no longer in range of your home WiFi, your phone can still receive notifications from the Owlet.
The Owlet App communicates with the Owlet Baby Monitor through a cloud-based system that can be accessed anywhere you have internet coverage on your smart device (as long as the Base Station is connected to Wifi and is in range of the Smart Sock).
The Base Station will send that info into the cloud through your home WiFi and your phone will access it from the cloud.