# Identify people

You need to identify a person using a mobile device before you can send them messages or track events for things they do in your app.

## Identify a person[](#identify)

Identifying a person:

1.  Adds or updates the person in your workspace. This is basically the same as an [`identify` call to our server-side API](/api/#operation/identify).
    
2.  Saves the person’s information on the device. Future calls to the SDK reference the identified person. For example, after you identify a person, any events that you track are automatically associated with that person.
    
3.  Associates the current device token with the the person.
    

You can only identify one customer at a time. The SDK “remembers” the most recently-identified customer. If you identify person A, and then call the identify function for person B, the SDK “forgets” person A and assumes that person B is the current app user. You can also [stop identifying a person](#clearIdentify), which you might do when someone logs off or stops using your app for a significant period of time.

An identify request takes the following parameters:

*   **userId** (required): The unique value representing a person—an ID or email address that represents a person in Customer.io (and your downstream destinations).
*   **traits** (Optional): Contains [attributesA key-value pair that you associate with a person or an object—like a person’s name, the date they were created in your workspace, or a company’s billing date etc. Use attributes to target people and personalize messages.](/journeys/attributes/) that you want to set for a person. The `traits` object accepts strings, enums, primitives (int, float, char, etc.), their boxed counterparts (Integer, Float, Character, etc.), arrays, collections, lists, sets, and maps.

We also offer a Kotlin serialization library that can help make it easier to set keys and values for the `traits` object.

```kotlin
CustomerIO.instance()
  .identify(
    userId = "USER_ID",
    traits = mapOf("first_name" to "firstName")
  )
```

### Update a person’s attributes[](#identify-again)

You store information about a person in Customer.io as [attributesA key-value pair that you associate with a person or an object—like a person’s name, the date they were created in your workspace, or a company’s billing date etc. Use attributes to target people and personalize messages.](/journeys/attributes/). When you call the `identify()` function, you can update a person’s attributes on the server-side.

If a person is already identified, and then updates their preferences, provides additional information about themselves, or performs other attribute-changing actions, you can update their attributes with `profileAttributes`.

```kotlin
CustomerIO.instance().setProfileAttributes(mapOf("favorite_food" to "pizza"))
```

You only need to pass the attributes that you want to set. For example, if you identify a new person with the attribute `"first_name": "Dana"`, and then you call `CustomerIO.instance().setProfileAttributes(mapOf("favorite_food" to "pizza"))`, the person’s `first_name` attribute will still be `Dana`. And Dana will now have a `favorite_food` attribute with the value `pizza`.

### Device attributes[](#device-attributes)

By default (if you don’t set `.autoTrackDeviceAttributes(false)` in your config), the SDK automatically collects a series of [attributesA key-value pair that you associate with a person or an object—like a person’s name, the date they were created in your workspace, or a company’s billing date etc. Use attributes to target people and personalize messages.](/journeys/attributes/) for each device. You can use these attributes in [segmentsA group of people who match a series of conditions. People enter and exit the segment automatically when they match or stop matching conditions.](/journeys/data-driven-segments/) and other campaign workflow conditions to target the device owner, just like you would use a person’s other attributes. You cannot, however, use device attributes to personalize messages with [liquidA syntax that supports variables, letting you personalize messages for your audience. For example, if you want to reference a person’s first name, you might use the variable `{{customer.first_name}}`.](/using-liquid) yet.

Along with these attributes, we automatically set a `last_used` timestamp for each device indicating when the device owner was last identified, and the `last_status` of a push notification you sent to the device. You can also set your own custom device attributes. You’ll see a person’s devices and each device’s attributes when you go to **Journeys > People > Select a person**, and click **Devices**.

[![device attributes on a person's profile](https://docs.customer.io/images/device-attributes.png)](#db82cfb11dbec1c42a9f938183dcedbd-lightbox)

 Your integration shows device attributes in the `context` object

When you inspect calls from the SDK (in your integration’s data inAn integration that feeds data *into* Customer.io. tab), you’ll see device information in the `context` object. We flatten the device attributes that you send into your workspace, so that they’re easier to use in [segmentsA segment is a group of people in your workspace. Use segments to trigger campaigns, track membership over time, or fine-tune your audience. There are two types of segments: data-driven and manual. Data-driven segments automatically update when people start or stop matching criteria. Manual segments are static.](/journeys/segments/). For example, `context.network.cellular` becomes `network_cellular`.

*   id string
    
    Required The device token.
    

#### Custom device attributes[](#custom-device-attributes)

When we collect device attributes, you can also set custom device attributes with the `deviceAttributes` method. You might do this to save app preferences, time zone, or other custom values specific to the device.

```kotlin
CustomerIO.instance().setDeviceAttributes(mapOf("key" to "value"))
```

However, before you set custom device attributes, consider whether the attribute is specific to the `device` or if it applies to a person more broadly. If you want an attribute to persist beyond the life of the device, you should [apply it to the person](#identify-again) rather than the device.

#### Disable automatic device attribute collection[](#disable-attributes)

By default, the SDK automatically collects the device attributes [defined above](#device-attributes). You can change your config to prevent the SDK from automatically collecting these attributes.

```kotlin
// set before you build
builder.autoTrackDeviceAttributes(false)
```

## Stop identifying a person[](#clearIdentify)

When a person logs out, or does something else to tell you that they no longer want to be tracked, you should stop identifying them.

Use `clearIdentify()` to stop identifying the previously identified person (if there was one).

```kotlin
// Future calls to the SDK are anonymous
CustomerIO.instance().clearIdentify()
```

### Identify a different person[](#identify-a-different-person)

If you want to identify a new person—like when someone switches profiles on a streaming app, etc—you can simply call `identify()` for the new person. The new person then becomes the currently-identified person, with whom all new information—messages, events, etc—is associated.