watchOS 4.2 (build 15S102) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2017-12-05T18:01:43Z. The update package is 145.55 MB. This is a delta (partial) update that requires 4.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 9a388734b8e5ed89c3f5dad52b4b735d4c3e17d2.zip.