There are several reasons why companies want to generate a new `userId` for each session. How this works on web is outlined [here](🔗). Please note that when you decide to randomize the userId as outlined below, the metric `Unique Users` will be equal to the `Plays` metrics.

# On Android

On Android there is a setting in the `AnalyticsConfig` called `randomizeUserId`. If this setting is set to `true`, then every time the collector is attached, a new `userId` will be generated. If a user is watching with a playlist, the user will have the same id for every video in the playlist.

If this setting is set to `false` then `Settings.Secure.ANDROID_ID` will be used as `userId`, which is **not** a random value! `false` is the default value.

# On iOS

On iOS the behaviour is consistent with the one on Android. In the `AnalyticsConfig` there is a setting called `randomizeUserId`. If this setting is set to `true`, then every time the collector is attached, a new `userId` will be generated.

If this setting is set to `false`, then a random ID is generated, stored in the `UserDefault Store`, and retrieved every time the user starts a session. `false` is the default value.