diff --git a/fw/Core/Inc/scd4x.h b/fw/Core/Inc/scd4x.h
index 921f9ee..426ff74 100644
--- a/fw/Core/Inc/scd4x.h
+++ b/fw/Core/Inc/scd4x.h
@@ -36,8 +36,9 @@ typedef enum {
 	SCD4X_START_PERIODIC_MEASUREMENT = 0x21B1,
 	SCD4X_READ_MEASUREMENT = 0xEC05,
 	SCD4X_STOP_PERIODIC_MEASUREMENT = 0x3F86,
-	SCD4X_GET_DATA_READY_STATUS = 0xe4b8,
-	SCD4X_PERFORM_FACTORY_RESET = 0x3632
+	SCD4X_GET_DATA_READY_STATUS = 0xE4B8,
+	SCD4X_PERFORM_FACTORY_RESET = 0x3632,
+	SCD4X_GET_SERIAL_NUMBER = 0x3682
 } scd4x_cmd_t;
 
 /*
diff --git a/fw/Core/Src/i2c.c b/fw/Core/Src/i2c.c
index 4279d27..8d68186 100644
--- a/fw/Core/Src/i2c.c
+++ b/fw/Core/Src/i2c.c
@@ -21,15 +21,11 @@ int8_t i2c_init(i2c_context_t *context)
 
 int8_t i2c_transmit(uint8_t address, uint8_t *buffer, int len)
 {
-	/* prevent interrupts during I2C communication (e.g. collision with MODBUS) */
-//	LL_LPUART_Disable(LPUART1);
-//	LL_LPUART_DisableIT_RXNE(LPUART1);
-//	__disable_irq();
 	LL_I2C_HandleTransfer(i2c_context->i2c, address, LL_I2C_ADDRSLAVE_7BIT, len,
 			LL_I2C_MODE_AUTOEND, LL_I2C_GENERATE_START_WRITE);
 	int i = 0;
-	// Autoend mode will raise STOP flag if NACK is detected
-	// (or if desired number of bytes is transmitted)
+	/* Autoend mode will raise STOP flag if NACK is detected
+	 * (or if desired number of bytes is transmitted) */
 	while (!LL_I2C_IsActiveFlag_STOP(i2c_context->i2c)) {
 		if (LL_I2C_IsActiveFlag_TXE(i2c_context->i2c)) {
 			if (i < len) {
@@ -38,25 +34,20 @@ int8_t i2c_transmit(uint8_t address, uint8_t *buffer, int len)
 		}
 	}
 	LL_I2C_ClearFlag_STOP(i2c_context->i2c);
-	if (LL_I2C_IsActiveFlag_NACK(i2c_context->i2c)) {
-		return I2C_ERROR_NACK;
-	}
 	if (len != i) {
-		// this will probably never happen, as NACK flag
-		// is raised everytime len != number of TXed bytes
+		/* If we detect NACK during transaction (before the end of the last byte) */
 		return I2C_ERROR_TX_INCOMPLETE;
 	}
-//	__enable_irq();
-//	LL_LPUART_Enable(LPUART1);
-//	LL_LPUART_EnableIT_RXNE(LPUART1);
+	/* NACK after last byte is ok */
+//	if (LL_I2C_IsActiveFlag_NACK(i2c_context->i2c)) {
+//
+//		return I2C_ERROR_NACK;
+//	}
 	return I2C_OK;
 }
 
 int8_t i2c_receive(uint8_t address, uint8_t *buffer, int len)
 {
-//	__disable_irq();
-//	LL_LPUART_Disable(LPUART1);
-//	LL_LPUART_DisableIT_RXNE(LPUART1);
 	LL_I2C_HandleTransfer(i2c_context->i2c, address, LL_I2C_ADDRSLAVE_7BIT, len,
 				LL_I2C_MODE_AUTOEND, LL_I2C_GENERATE_START_READ);
 	int i = 0;
@@ -71,8 +62,6 @@ int8_t i2c_receive(uint8_t address, uint8_t *buffer, int len)
 	if (len != i) {
 		return I2C_ERROR_RX_INCOMPLETE;
 	}
-//	__enable_irq();
-//	LL_LPUART_Enable(LPUART1);
-//	LL_LPUART_EnableIT_RXNE(LPUART1);
-	return I2C_OK; // TODO error detection
+
+	return I2C_OK;
 }
diff --git a/fw/Core/Src/main.c b/fw/Core/Src/main.c
index 75d5fed..a291fcf 100644
--- a/fw/Core/Src/main.c
+++ b/fw/Core/Src/main.c
@@ -187,7 +187,7 @@ int main(void)
   MX_TIM21_Init();
   MX_TIM2_Init();
   MX_TIM22_Init();
-  MX_IWDG_Init();
+//  MX_IWDG_Init();
   /* USER CODE BEGIN 2 */
 
   /* Turn on MAGENTA LED to signal startup state */
@@ -246,25 +246,23 @@ int main(void)
   LL_mDelay(2000);
 
   scd4x_start_periodic_measurement();
-  uint8_t scd4x_is_connected = 1;
+  uint8_t scd4x_is_connected = 0;
   uint8_t sps30_is_connected = 0;
   /* USER CODE END 2 */
 
   /* Infinite loop */
   /* USER CODE BEGIN WHILE */
-  /*uint8_t scd4x_is_connected = 0;
   if (scd4x_start_periodic_measurement() == SCD4X_OK)
   {
 	  scd4x_is_connected = 1;
-  }*/
+  }
 
   /* Attempt to start SPS30 measurement and check if it's connected */
-  /*sps30_reset();
-  uint8_t sps30_is_connected = 0;
+  sps30_reset();
   if (sps30_start_measurement() == SPS30_OK)
   {
 	  sps30_is_connected = 1;
-  }*/
+  }
 
   /* Wait 1000ms for sensors initialization */
   /* SHT4x Init Time: max 1 	ms 	(datasheet pg. 8) */
diff --git a/fw/Core/Src/scd4x.c b/fw/Core/Src/scd4x.c
index c8ab1d0..e5c4645 100644
--- a/fw/Core/Src/scd4x.c
+++ b/fw/Core/Src/scd4x.c
@@ -17,13 +17,22 @@ int8_t scd4x_send_cmd(scd4x_cmd_t cmd)
 	buffer[0] = cmd >> 8;
 	buffer[1] = cmd & 0x00ff;
 	result = i2c_transmit(SCD4X_I2C_ADDRESS<<1, buffer, 2);
-	if (result != I2C_OK) {
+	if (result == I2C_ERROR_TX_INCOMPLETE) {
 		return SCD4X_ERROR;
 	}
 
+	/* Sensirion sensors return NACK after last byte (so NACK at the end is ok) */
 	return SCD4X_OK;
 }
 
+int8_t scd4x_get_serial(uint8_t serial[6])
+{
+	uint8_t buffer[16];
+
+	scd4x_send_cmd(SCD4X_GET_SERIAL_NUMBER);
+	i2c_receive(SCD4X_I2C_ADDRESS << 1, buffer, 9);
+}
+
 int8_t scd4x_read_data(uint8_t *buffer, int len)
 {
 	return SCD4X_OK;