The Diary is a device created during The Beautiful Days. It became in an essential accessory since they can use it to control their androids (give to them orders), their homes (turn the light or open the windows), the electronic clothes (change the color) and their lives (they have something like Instagram or Facebook but in local mode). They hadn’t Internet, so the Diary worked with television and radio waves.
This device has the aspect of a Smartphone but more futuristic whit the design of stained glass. The users had to touch in the right places of stained glass to unblock the Diary.
In the present, these devices are used to control the robots, the androids, and other electronic devices. Also, they are used as maps and encyclopedias. Groups like SPTS or some Hospital Shelters like The Farm used the radio to send messages with the latest news about the Toxin, the cure, new mutations or new enemies.
In the game, this device is also the menu inside the game. Like in Far Cry 2 that the menu was a diary.