diff --git a/scd4x.py b/scd4x.py
index f4fc409..aa37227 100644
--- a/scd4x.py
+++ b/scd4x.py
@@ -4,8 +4,8 @@
 #
 # SPDX-License-Identifier: MIT
 #
-# this version: also Copyright (c) 2022-2024 peter-l5
-# build version: v103
+# this version: also Copyright (c) 2022-2026 peter-l5, khaylenko
+# build version: v107
 
 """
 `micropython_scd4x`
@@ -14,7 +14,7 @@
 Driver for Sensirion SCD4X CO2 sensor
 
 
-* Author(s): ladyada, peter-l5
+* Author(s): ladyada, peter-l5, khaylenko
 
 Implementation Notes
 --------------------
@@ -34,7 +34,7 @@
 from micropython import const
 import struct
 
-__version__ = "v103"
+__version__ = "v107"
 __repo__ = "https://github.com/peter-l5/MicroPython_SCD4X"
 
 SCD4X_DEFAULT_ADDR = 0x62
@@ -56,6 +56,7 @@
 _SCD4X_PERSISTSETTINGS = const(0x3615)
 _SCD4X_GETASCE = const(0x2313)
 _SCD4X_SETASCE = const(0x2416)
+_SCD4X_SENSORVARIANT = const(0x202F)
 
 
 class SCD4X:
@@ -94,12 +95,13 @@ class SCD4X:
 
     """
 
-    def __init__(self, i2c_bus: I2C, address: int = SCD4X_DEFAULT_ADDR) -> None:
-        print("__init__ :", dir())
-        print("address : %x" % address)
-        print("i2c_bus : ", i2c_bus)
+    def __init__(self, i2c_bus: I2C, address: int = SCD4X_DEFAULT_ADDR, debug_info: bool = True) -> None:
+        if debug_info:
+            print("__init__ :", dir())
+            print("address : %x" % address)
+            print("i2c_bus : ", i2c_bus)
+            print(i2c_bus)
         self.address = address
-        print(i2c_bus)
         self.i2c_device = i2c_bus
         self._buffer = bytearray(18)
         self._cmd = bytearray(2)
@@ -191,14 +193,27 @@ def self_calibration_enabled(self) -> bool:
     def self_calibration_enabled(self, enabled: bool) -> None:
         self._set_command_value(_SCD4X_SETASCE, enabled)
 
-    def self_test(self) -> None:
+    def self_test(self) -> dict:
         """Performs a self test, takes up to 10 seconds"""
         self.stop_periodic_measurement()
         self._send_command(_SCD4X_SELFTEST, cmd_delay=10)
         self._read_reply(self._buffer, 3)
-        if (self._buffer[0] != 0) or (self._buffer[1] != 0):
-            raise RuntimeError("Self test failed")
-
+        
+        code = (self._buffer[0] << 8) | self._buffer[1]
+        
+        if code == 0:
+            result = 'Test passed'
+        elif code == 512:
+            result = 'Sensor Element Failure'
+        elif code == 1024:
+            result = 'Heater Failure'
+        elif code == 2048:
+            result = 'Measurement Circuit / Out of Range'            
+        else:
+            result = 'Unknown'
+        
+        return {'result': result, 'code': code}
+        
     def _read_data(self) -> None:
         """Reads the temp/hum/co2 from the sensor and caches it"""
         self._send_command(_SCD4X_READMEASUREMENT, cmd_delay=0.001)
@@ -217,18 +232,36 @@ def data_ready(self) -> bool:
         return not ((self._buffer[0] & 0x07 == 0) and (self._buffer[1] == 0))
 
     @property
-    def serial_number(self) -> Tuple[int, int, int, int, int, int]:
-        """Request a 6-tuple containing the unique serial number for this sensor"""
+    def serial_number(self) -> int:
+        """Request the unique serial number for this sensor."""
         self._send_command(_SCD4X_SERIALNUMBER, cmd_delay=0.001)
         self._read_reply(self._buffer, 9)
-        return (
-            self._buffer[0],
-            self._buffer[1],
-            self._buffer[3],
-            self._buffer[4],
-            self._buffer[6],
-            self._buffer[7],
-        )
+        
+        word0 = (self._buffer[0] << 8) | self._buffer[1]
+        word1 = (self._buffer[3] << 8) | self._buffer[4]
+        word2 = (self._buffer[6] << 8) | self._buffer[7]
+                
+        return word0 << 32 | word1 << 16 | word2
+    
+    @property
+    def sensor_variant(self) -> dict:
+        """Request a string containing the sensor variant"""
+        self._send_command(_SCD4X_SENSORVARIANT, cmd_delay=0.001)
+        self._read_reply(self._buffer, 3)
+        
+        raw = (self._buffer[0] << 8) | self._buffer[1]
+        extracted = (raw & 0xF000) >> 12
+        
+        if extracted == 0:
+            variant = 'SCD40'
+        elif extracted == 1:
+            variant = 'SCD41'
+        elif extracted == 5:
+            variant = 'SCD43'
+        else:
+            variant = 'Unknown'
+        
+        return {'variant': variant, 'raw': raw}
 
     def stop_periodic_measurement(self) -> None:
         """Stop measurement mode"""