Discord's new Mobile Indicator

The mobile indicator is a feature that recently landed on Stable versions of Discord (January 16, 2019). It gives a phone icon next to a given user when they supposedly are using their phone.

You can set yourself to idle/dnd/invisible to hide the mobile indicator. It is also possible to patch the Android app.

Detecting phone usage

The Gateway's IDENTIFY packet contains a properties field, containing os, browser and device fields. Discord uses that information to know when your phone client and only your phone client has connected to Discord, from there they send the extended presence object.

The exact field that is checked is the browser field. If it's set to Discord Android on desktop, the mobile indicator is is triggered by the desktop client. If it's set to Discord Client on mobile, the mobile indicator is not triggered by the mobile client.

The specific values for the os, browser and device fields can change from time to time.

At the time of writing, bots can spoof those fields and have the mobile indicator set.

Presence with mobile field

Presence objects come with a mobile field, which is a boolean telling if the user being referenced by the presence is on mobile or not. It is not known if the field is optional or not, for all intents and purposes, assume it is.