https://wccftech.com/modern-warfare-has-an-optional-tamagunchi-add-on-for-your-wristwatch-in-multiplayer/

Modern Warfare’s multiplayer modes allow player characters to wear functioning wristwatches with different functionalities, as revealed to Game Informer by Geoff Smith, Multiplayer Design Director at Infinity Ward.

We put in a watch pretty early on; one of our coders got really excited about it and over a weekend synced up a dev kit to have the actual time on the watch, so it actually tells the real time from your kit. Then that just kind of kept growing into more and more madness.