The DA14683 is fantastic. I played a bit with an eval. board and it's really good for it's price vs. features (~$3 for 250 pcs. at Mouser). But soon the idea of releasing code for it as Open Source faded away, since you need to sign an SLA (https://support.dialog-semiconductor.com/connectivity/reques...), that limits the way source code based on their in SDK is released (only to your customer, in an only “need to know” basis). I hate when this happens.

I wonder how the creator of this watch managed to publish the source code, including the Dialog SDK; if there is a backdoor I am missing.