---
schema_version: "1"
id: 277884d135d79e12d8353511c06aca393b0930cd0cdc27047e87529cdd963b40
title: Contacts and Devices
collection: admin
version: current
locale: en-us
portal_url: https://docs.salesforce.com/admin/current/en-us/mktg/264-0-0/mc_mp_contact_or_subscriber_key.md
canonical_url: https://help.salesforce.com/s/articleView?id=mktg.mc_mp_contact_or_subscriber_key.htm&release=264.0.0&type=5
source_site: help.salesforce.com
content_type: documentation
content_hash: eaf6cce618f336d3a077b8ee6a5ccb49a43ef15f313a88f38296e815b24c5f6d
description: The contact key, also known as a subscriber key, is a unique identifier for a contact in MobilePush. Use this value to associate cross-channel addresses and subscriptions for a single contact. You can use the same key for a contact across multiple channels, such as email, SMS, and push messaging.
products:
  - Marketing
  - Marketing Cloud Engagement
release: "264"
---
# Contacts and Devices

The contact key, also known as a subscriber key, is a unique identifier for a contact in MobilePush. Use this value to associate cross-channel addresses and subscriptions for a single contact. You can use the same key for a contact across multiple channels, such as email, SMS, and push messaging.

Use a unique value for the contact key. Examples of unique values include universally unique identifiers (UUIDs), an email address, or a mobile phone number. If you don’t specify a contact key, MobilePush generates a UUID when the SDK is initialized. In cases where anonymous users aren’t relevant, wait to initialize the SDK until your desired contact key is determined.

You can update a record’s contact key at any time. For example, you can associate a user with the same key you use to identify email subscribers.

In Marketing Cloud Engagement, a device ID is a unique identifier for one mobile device. A contact can have multiple mobile devices, but a device can’t have multiple contacts. If a new contact logs in to a device, Marketing Cloud Engagement associates the device with the new contact key. It takes about 15 minutes for the device to be associated with the new contact key.