> For the complete documentation index, see [llms.txt](https://docs.cotter.app/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.cotter.app/sdk-reference/android.md).

# Android

## Complete Guides

#### **Sign in with Device**

Allow users to login automatically from a device that they trust.

{% content-ref url="/pages/-M14g3WtD4o3ZG9N2j9G" %}
[Sign In with Device](/sdk-reference/android/older-sdk-version/android-sdk.md)
{% endcontent-ref %}

#### Sign in with Email/Phone Number

Authenticate users by sending a Magic Link or OTP via email, SMS, or WhatsApp.

{% content-ref url="/pages/-M0et2D8qa-mVoDh-tjp" %}
[Sign In with Email/Phone Number](/sdk-reference/android/android-sdk-1.md)
{% endcontent-ref %}

#### Add Biometric/Pin

Add a second layer to protect your mobile app using Biometric or Pin.

{% content-ref url="/pages/-M0RaVb\_ggDYyCQyIUXy" %}
[Biometric/Pin](/sdk-reference/android/android-sdk-2.md)
{% endcontent-ref %}