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

# Detect IMEI events and get notified when a SIM has moved to another device

> Track when SIMs are moved between devices using IMEI and TAC change detection. IMEI and IMEI TAC change events are available in [Event monitoring](/guides/cloud-and-tools/event-monitoring-and-alerts-overview) and can be used to create [alerts](/guides/cloud-and-tools/event-monitoring-and-alerts-overview) to notify you when a SIM is moved to a new device.

## What is IMEI and IMEI TAC?

Every cellular connected device has an [IMEI (International Mobile Equipment Identity)](https://en.wikipedia.org/wiki/International_Mobile_Equipment_Identity) number, which is used to identify the hardware that is being connected to the network. This is very useful when it comes to mapping SIMs to specific devices and detecting when a SIM is being used in a new device. Hologram can always trace a SIM using [your dashboard](https://dashboard.hologram.io/) and determine what device it's being used in by viewing session data as described [in this guide](/dashboard/usage/usage-single-sim).

The [Type Allocation Code (TAC)](https://en.wikipedia.org/wiki/Type_Allocation_Code) is the initial eight-digit portion of the IMEI, and it indicates the manufacturer, make, and model of the device. An `_IMEI_TAC_CHANGE_` message means that the new IMEI has a completely different manufacturer, make, or model than the old IMEI. An `_IMEI_CHANGE_` message indicates that the new device has the same manufacturer, make, and model as the old device.

## How does Hologram detect IMEI and IMEI TAC changes?

Hologram has built-in IMEI detection that keeps track of the IMEI of the device used with the SIM as provided by networks during data sessions. These events are tracked and recorded in the [Event monitoring](/guides/cloud-and-tools/event-monitoring-and-alerts-overview) section of your dashboard, and are created:

<Frame>
  <img src="https://mintcdn.com/hologram-b29df2a6/gBXuuJ66IPyI_nhw/images/event-monitoring/events-imei-change.webp?fit=max&auto=format&n=gBXuuJ66IPyI_nhw&q=85&s=806bd40cfa8b59fb4bf5c737f3538767" alt="Activity console showing IMEI change detection messages with tags" width="2880" height="776" data-path="images/event-monitoring/events-imei-change.webp" />
</Frame>

* When a SIM is **first connected** by sending a message and attaching an `_IMEI_FIRST_` tag.
* When a SIM is connected using a **different IMEI** compared to the previous session by sending a message describing the change and attaching an `_IMEI_CHANGE_` tag.
* When a SIM is connected using a **different modem model (different IMEI and TAC)** by sending a message describing the change and attaching an `_IMEI_TAC_CHANGE_` tag.

## How I get notified when a SIM is moved to a new device?

You can create a new Alert to receive notifications about IMEI changes.

<Steps>
  <Step title="Navigate to the Alerts page">
    Navigate to the **Event monitoring** section in the main menu and open the **Alerts** page. Press the **Create alert** button in the top right corner of the page.
  </Step>

  <Step title="Create a new alert">
    In the list of event types that appears, you can choose to subscribe to "First IMEI recognized" or "Hardware change (IMEI or TAC changed)" events.

    <Frame>
      <img src="https://mintcdn.com/hologram-b29df2a6/gBXuuJ66IPyI_nhw/images/event-monitoring/alerts-create-imei-alert.webp?fit=max&auto=format&n=gBXuuJ66IPyI_nhw&q=85&s=2ea449e98b75061ffa781e0fda0177ae" alt="Create alert form showing topic selection" width="2880" height="1083" data-path="images/event-monitoring/alerts-create-imei-alert.webp" />
    </Frame>
  </Step>

  <Step title="Configure the alert">
    Configure the notification settings to send notifications to email, SMS, or webhooks when specific events occur.
  </Step>
</Steps>