How to find serial number of Android device?

TelephonyManager tManager = (TelephonyManager)myActivity.getSystemService(Context.TELEPHONY_SERVICE);
String uid = tManager.getDeviceId();

getSystemService is a method from the Activity class. getDeviceID() will return the MDN or MEID of the device depending on which radio the phone uses (GSM or CDMA).

Each device MUST return a unique value here (assuming it's a phone). This should work for any Android device with a sim slot or CDMA radio. You're on your own with that Android powered microwave ;-)

String serial = null; 

try {
    Class<?> c = Class.forName("android.os.SystemProperties");
    Method get = c.getMethod("get", String.class);
    serial = (String) get.invoke(c, "ro.serialno");
} catch (Exception ignored) {
}

This code returns device serial number using a hidden Android API.

String deviceId = Settings.System.getString(getContentResolver(),
                                Settings.System.ANDROID_ID);

Although, it is not guaranteed that the Android ID will be an unique identifier.

The IMEI is good but only works on Android devices with phone. You should consider support for Tablets or other Android devices as well, that do not have a phone.

You have some alternatives like: Build class members, BT MAC, WLAN MAC, or even better - a combination of all these.

I have explained these details in an article on my blog, see: http://www.pocketmagic.net/?p=1662

Build.SERIAL is the simplest way to go, although not entirely reliable as it can be empty or sometimes return a different value (proof 1, proof 2) than what you can see in your device's settings.

There are several ways to get that number depending on the device's manufacturer and Android version, so I decided to compile every possible solution I could found in a single gist. Here's a simplified version of it :

public static String getSerialNumber() {
    String serialNumber;

    try {
        Class<?> c = Class.forName("android.os.SystemProperties");
        Method get = c.getMethod("get", String.class);

        serialNumber = (String) get.invoke(c, "gsm.sn1");
        if (serialNumber.equals(""))
            serialNumber = (String) get.invoke(c, "ril.serialnumber");
        if (serialNumber.equals(""))
            serialNumber = (String) get.invoke(c, "ro.serialno");
        if (serialNumber.equals(""))
            serialNumber = (String) get.invoke(c, "sys.serialnumber");
        if (serialNumber.equals(""))
            serialNumber = Build.SERIAL;

        // If none of the methods above worked
        if (serialNumber.equals(""))
            serialNumber = null;
    } catch (Exception e) {
        e.printStackTrace();
        serialNumber = null;
    }

    return serialNumber;
}

Starting in Android 10, apps must have the READ_PRIVILEGED_PHONE_STATE privileged permission in order to access the device's non-resettable identifiers, which include both IMEI and serial number.

Affected methods include the following:

Build getSerial() TelephonyManager getImei() getDeviceId() getMeid() getSimSerialNumber() getSubscriberId()

READ_PRIVILEGED_PHONE_STATE is available for platform only

public static String getManufacturerSerialNumber() {
  String serial = null; 
  try {
      Class<?> c = Class.forName("android.os.SystemProperties");
      Method get = c.getMethod("get", String.class, String.class);
      serial = (String) get.invoke(c, "ril.serialnumber", "unknown");
  } catch (Exception ignored) {}
  return serial;
}

Works on API 29 and 30, tested on Samsung galaxy s7 s9 Xcover