Apple Watch Series 3 runs WatchOS 4. Auto-exchanging between Bluetooth, Wi-Fi and cell is overseen by new W2 remote chip. To get notices from outsider applications in the cloud, your iPhone should be fueled up some place so the Watch can speak with it by means of the cloud.
https://spinonews.com/2018/01/02/popular-wearable-technology-in-2017/
