Apple Watch Series 3 requires an iPhone 6s or later with iOS 14 or later.
1ISO standard 22810:2010. Appropriate for shallow-water activities like swimming. Submersion below shallow depth and high-velocity water activities not recommended.
2 To use Emergency SOS, your iPhone needs to be nearby. If your iPhone isn’t nearby, your Apple Watch needs to be connected to a known Wi-Fi network and you must set up Wi-Fi Calling.