The Genome Codex (ゲノム コデックス genomu kodekkusu ) is a device that was programmed to monitor the wearer's health, track any E-Type BOW and to receive incoming calls from other people. It is featured in Resident Evil 7: Biohazard.
Mia and Alan wore them while transporting Eveline on a ship in 2014. Mia loses hers by the time she is trying to avoid being captured by the Bakers. Ethan Winters is given one by Zoe Baker in 2017. Before the defeat of Eveline, Ethan receives a call from Redfield on his.
The Genome Codex functions passively when the player character has it on them. It will display the player's health represented by an electrocardiogram (ECG) displaying four potential colors; green, yellow, orange, and red. Bringing up the inventory screen or guarding will make the character hold up their arm and put the watch in focus.
During the main game, the player will receive it after the Guest House section and have it for the rest of the game. There are scripted events where it will identify D-Series cases such as after the first fight with Marguerite Baker. Mia doesn't have it during the "Mia" tape or when she's looking for Ethan in the tanker.
It is seen later when Mia watches a tape in the tanker section of the main game, it will track the distance of Eveline on-board the tanker, as well as receive incoming calls from Alan. While standing idle, Mia will raise her aim to put it in view.
Ethan will also have it during Ethan Must Die.