diff --git a/fw/Core/Src/main.c b/fw/Core/Src/main.c
index 39cd156..cb0ab20 100644
--- a/fw/Core/Src/main.c
+++ b/fw/Core/Src/main.c
@@ -1049,6 +1049,12 @@ int8_t modbus_slave_callback(modbus_transaction_t *transaction)
 					case REGISTER_NUM_RH_SCD4x:
 						transaction->input_registers[i] = (uint16_t)RH_SCD4x;
 						break;
+					case REGISTER_NUM_SERIAL_NUMBER_1:
+						transaction->input_registers[i] = (uint16_t)sensor_config.serial_number_1;
+						break;
+					case REGISTER_NUM_SERIAL_NUMBER_2:
+						transaction->input_registers[i] = (uint16_t)sensor_config.serial_number_2;
+						break;
 					default:
 						return MODBUS_ERROR_FUNCTION_NOT_IMPLEMENTED;
 				}