# Cross-device identity reconciliation

When users interact with your product across multiple devices — web browsers, mobile apps, connected TVs, and tablets — each device typically generates its own anonymous `fides_user_device_id`. Without identity linking, this creates fragmented consent records: the same person may appear as four separate users with conflicting privacy preferences.

Fides solves this through **cross-device identity reconciliation**. When a user authenticates (e.g., logs in with an email address), Fides merges all associated device identities into a single unified profile. From that point on, any preference query — by device ID or email — returns the same consistent result.

This workflow uses the **pre-verified** consent endpoint (`PATCH /api/v1/privacy-preferences/pre-verified`), which accepts both a `fides_user_device_id` and a verified identity (such as `email`) in a single call. This is the recommended approach for server-side integrations where the user's identity has already been verified by your authentication system.

## Walkthrough [Permalink for this section](/content/docs/consent/concepts/advanced/cross-device-identity#walkthrough/index.html)

Step through the scenario below to see how four anonymous device records are progressively linked into a single identity as the user authenticates on each platform.

Website

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Mobile App

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Connected TV

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Tablet App

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Unified Identity

### The Problem: Fragmented Consent

Cookie House Network operates across web, mobile, connected TV, and tablet. Each platform collects privacy preferences independently using anonymous device IDs. The same user may have **conflicting preferences** scattered across four separate records.

## How it works [Permalink for this section](/content/docs/consent/concepts/advanced/cross-device-identity#how-it-works/index.html)

1. **Anonymous collection** — Each platform saves consent via `PATCH /api/v1/privacy-preferences` using only the device's `fides_user_device_id`. At this stage, Fides treats each device as a separate user.

2. **Authenticated linking** — When a user logs in, the platform calls `PATCH /api/v1/privacy-preferences/pre-verified` with both the `fides_user_device_id` and a verified identifier (e.g., `email`). Fides creates or extends a unified identity graph that links the device ID to the email.

3. **Preference merging** — As additional devices authenticate with the same email, they are merged into the existing identity. The most recent preference associated with the unified identity becomes the canonical value.

4. **Consistent reads** — `GET /api/v1/current-privacy-preferences` with any linked identifier (device ID or email) returns the same unified preference record.

5. **Cross-device propagation** — When the user updates their preference on any linked device, the updated value is available to all other devices on their next read from Fides.

## Related resources [Permalink for this section](/content/docs/consent/concepts/advanced/cross-device-identity#related-resources/index.html)

- [Consent API](/content/docs/consent/reference/consent-api/index.html) — Full reference for the V1 consent endpoints
- [Bidirectional Consent](/content/docs/consent/guides/bidirectional-consent/index.html) — How Fides propagates consent to third-party systems
- [Mobile SDK](/content/docs/privacy-center-fidesjs/mobile-sdk/index.html) — Integrating consent collection in mobile applications

[Data Use to Regulation Mapping](/content/docs/consent/concepts/regulations/data-use-to-regulation-mapping "Data Use to Regulation Mapping"/index.html) [Consent Signals](/content/docs/consent/concepts/advanced/consent-signals "Consent Signals"/index.html)