I need to register user devices on server with an unique identifier that be a constant value and doesn't change in the future.

I can't find a good solution to get unique id from all devices (with/without simcard).

Secure.ANDROID_ID: Secure.ANDROID_ID is not unique and can be null or change on factory reset.

String m_androidId = Secure.getString(getContentResolver(), Secure.ANDROID_ID); IMEI: IMEI is dependent on the Simcard slot of the device, so it is not possible to get the IMEI for the devices that do not use Simcard.