System - Get IMEI Number

//1

public String getIMEI(Activity activity) {
    android.telephony.TelephonyManager telephonyManager = (android.telephony.TelephonyManager) activity.getSystemService(Context.TELEPHONY_SERVICE);
    return telephonyManager.getDeviceId();
}

//2
public String getDeviceUniqueID(Activity activity){
    String device_unique_id = android.provider.Settings.Secure.getString(activity.getContentResolver(),
    android.provider.Settings.Secure.ANDROID_ID);
    return device_unique_id;
}

//3
public String getIMEI(Context context){
    android.telephony.TelephonyManager mngr = (android.telephony.TelephonyManager) context.getSystemService(context.TELEPHONY_SERVICE);
    String imei = mngr.getDeviceId();
    return imei;
}

//Need Permission READ_PHONE_STATE