> ## Documentation Index
> Fetch the complete documentation index at: https://docs.authsignal.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Device tracking

> Use the Web SDK to remember users' devices and create rules for adaptive MFA.

The Web SDK client exposes an `anonymousId` property which can be used as the `deviceId` value when tracking an action.

<CodeGroup>
  ```js Web theme={null}
  const deviceId = authsignal.anonymousId;
  ```
</CodeGroup>

This value is persisted as a cookie on the domain where you have initialized the Web SDK client. The name of the cookie is **\_\_as\_aid**.

You can pass this value to your server and into a track request using a Server SDK in order to use [rules based on device](/actions-rules/rules/getting-started#using-rules-with-actions).