diff --git a/docs/devices/H5140.md b/docs/devices/H5140.md
new file mode 100644
index 00000000..31927157
--- /dev/null
+++ b/docs/devices/H5140.md
@@ -0,0 +1,12 @@
+# Govee H5140
+
+|Model Id|[H5140](https://github.com/theengs/decoder/blob/development/src/devices/H5140_json.h)|
+|-|-|
+|Brand|Govee|
+|Model|Smart CO2 Monitor|
+|Short Description|Air quality monitor with temperature, humidity and CO2|
+|Communication|BLE broadcast|
+|Frequency|2.4Ghz|
+|Power Source|USB-C|
+|Exchanged Data|temperature, humidity, CO2|
+|Encrypted|No|
diff --git a/src/decoder.h b/src/decoder.h
index 4772d73f..6a2c048b 100644
--- a/src/decoder.h
+++ b/src/decoder.h
@@ -92,6 +92,7 @@ class TheengsDecoder {
     H5074,
     H5102,
     H5106,
+    H5140,
     H5179,
     H5179_N,
     HHCCJCY10,
diff --git a/src/devices.h b/src/devices.h
index 7763e683..869b6c7f 100644
--- a/src/devices.h
+++ b/src/devices.h
@@ -36,6 +36,7 @@
 #include "devices/H5074_json.h"
 #include "devices/H5102_json.h"
 #include "devices/H5106_json.h"
+#include "devices/H5140_json.h"
 #include "devices/H5179_json.h"
 #include "devices/HHCCJCY10_json.h"
 #include "devices/HHCCJCY01HHCC_json.h"
@@ -188,6 +189,7 @@ const char* _devices[][2] = {
     {_H5074_json, _H5074_json_props},
     {_H5102_json, _H5102_json_props},
     {_H5106_json, _H5106_json_props},
+    {_H5140_json, _H5140_json_props},
     {_H5179_json, _H5179_json_props},
     {_H5179_json_N, _H5179_json_props},
     {_HHCCJCY10_json, _HHCCJCY10_json_props},
diff --git a/src/devices/H5140_json.h b/src/devices/H5140_json.h
new file mode 100644
index 00000000..2bf472ff
--- /dev/null
+++ b/src/devices/H5140_json.h
@@ -0,0 +1,69 @@
+const char* _H5140_json = "{\"brand\":\"Govee\",\"model\":\"Smart CO2 Monitor\",\"model_id\":\"H5140\",\"tag\":\"0f03\",\"condition\":[\"name\",\"contain\",\"GV5140\",\"&\",\"manufacturerdata\",\">=\",20,\"index\",0,\"01000101\"],\"properties\":{\"tempc\":{\"decoder\":[\"value_from_hex_data\",\"manufacturerdata\",8,6,false,false],\"post_proc\":[\"/\",10000]},\"hum\":{\"decoder\":[\"value_from_hex_data\",\"manufacturerdata\",8,6,false,false],\"post_proc\":[\"&\",2147483647,\"%\",1000,\"/\",10]},\"co2\":{\"decoder\":[\"value_from_hex_data\",\"manufacturerdata\",14,4,false,false]}}}";
+/* R""""(
+{
+   "brand":"Govee",
+   "model":"Smart CO2 Monitor",
+   "model_id":"H5140",
+   "tag":"0f03",
+   "condition":["name", "contain", "GV5140", "&", "manufacturerdata", ">=", 20, "index", 0, "01000101"],
+   "properties":{
+      "tempc":{
+         "decoder":["value_from_hex_data", "manufacturerdata", 8, 6, false, false],
+         "post_proc":["/", 10000]
+      },
+      "hum":{
+         "decoder":["value_from_hex_data", "manufacturerdata", 8, 6, false, false],
+         "post_proc":["&", 2147483647, "%", 1000, "/", 10]
+      },
+      "co2":{
+         "decoder":["value_from_hex_data", "manufacturerdata", 14, 4, false, false]
+      }
+   }
+})"""";*/
+
+/*
+ * Govee H5140 Smart CO2 Monitor - BLE Manufacturer Data Format
+ * =============================================================
+ *
+ * Advertisement name pattern: GV5140XXXX (where XXXX is device suffix)
+ * Manufacturer data: 20 hex characters (10 bytes)
+ *
+ * Byte layout:
+ *   Positions 0-7:   01000101 (constant header)
+ *   Positions 8-13:  XXXXXX (24-bit combined temp/humidity)
+ *   Positions 14-17: YYYY (16-bit CO2 in ppm, big-endian)
+ *   Positions 18-19: 00 (padding/unknown)
+ *
+ * Decoding formulas:
+ *   - temp_celsius = 24bit_value / 10000
+ *   - humidity_percent = (24bit_value % 1000) / 10
+ *   - co2_ppm = 16bit_value
+ *
+ * Example: 0100010103fcbf044c00
+ *   - Header: 01000101
+ *   - Temp/Hum: 03fcbf = 261311 decimal
+ *     - Temperature: 261311 / 10000 = 26.13°C (79.04°F)
+ *     - Humidity: (261311 % 1000) / 10 = 31.1%
+ *   - CO2: 044c = 1100 ppm
+ *
+ * Tested with OpenMQTTGateway on ESP32
+ */
+
+const char* _H5140_json_props = "{\"properties\":{\"tempc\":{\"unit\":\"°C\",\"name\":\"temperature\"},\"hum\":{\"unit\":\"%\",\"name\":\"humidity\"},\"co2\":{\"unit\":\"ppm\",\"name\":\"carbon_dioxide\"}}}";
+/*R""""(
+{
+   "properties":{
+      "tempc":{
+         "unit":"°C",
+         "name":"temperature"
+      },
+      "hum":{
+         "unit":"%",
+         "name":"humidity"
+      },
+      "co2":{
+         "unit":"ppm",
+         "name":"carbon_dioxide"
+      }
+   }
+})"""";*/
diff --git a/tests/BLE/test_ble.cpp b/tests/BLE/test_ble.cpp
index 833dad55..bf2b444f 100644
--- a/tests/BLE/test_ble.cpp
+++ b/tests/BLE/test_ble.cpp
@@ -237,6 +237,9 @@ const char* expected_mfg[] = {
     "{\"brand\":\"Victron Energy\",\"model\":\"Smart Battery Sense\",\"model_id\":\"VICTSBS\",\"type\":\"ENRG\",\"track\":true,\"volt\":12.99,\"tempc\":17.5,\"tempf\":63.5,\"alarm_reason\":0}",
     "{\"brand\":\"Victron Energy\",\"model\":\"Smart Battery Sense\",\"model_id\":\"VICTSBS\",\"type\":\"ENRG\",\"track\":true,\"volt\":14.01,\"tempc\":17.5,\"tempf\":63.5,\"alarm_reason\":0}",
     "{\"brand\":\"Victron Energy\",\"model\":\"Smart Battery Sense\",\"model_id\":\"VICTSBS\",\"type\":\"ENRG\",\"track\":true,\"volt\":12.22,\"tempc\":22.5,\"tempf\":72.5,\"alarm_reason\":0}",
+    "{\"brand\":\"Govee\",\"model\":\"Smart CO2 Monitor\",\"model_id\":\"H5140\",\"type\":\"AIR\",\"cidc\":false,\"acts\":true,\"tempc\":26.1311,\"tempf\":79.03598,\"hum\":31.1,\"co2\":1100}",
+    "{\"brand\":\"Govee\",\"model\":\"Smart CO2 Monitor\",\"model_id\":\"H5140\",\"type\":\"AIR\",\"cidc\":false,\"acts\":true,\"tempc\":15.56,\"tempf\":60.008,\"hum\":60,\"co2\":500}",
+    "{\"brand\":\"Govee\",\"model\":\"Smart CO2 Monitor\",\"model_id\":\"H5140\",\"type\":\"AIR\",\"cidc\":false,\"acts\":true,\"tempc\":23.8048,\"tempf\":74.84864,\"hum\":4.8,\"co2\":1700}",
 };
 
 const char* expected_name_uuid_mfgsvcdata[] = {
@@ -828,6 +831,9 @@ const char* test_mfgdata[][3] = {
     {"Victron Smart Battery Sense", "",                         "e1021180a5a302ffff7bffff130500008971feff7fffffffff"},
     {"Victron Smart Battery Sense", "",                         "e1021180a5a302ffff7bffff790500008971feff7fffffffff"},
     {"Victron Smart Battery Sense", "",                         "e1021100a4a302ffff7cffffc60400007d73feff7fffffffff"},
+    {"H5140", "GV5140_1234", "0100010103fcbf044c00"},
+    {"H5140", "GV5140_1234", "01000101025fd001f400"},
+    {"H5140", "GV5140_1234", "0100010103a1e006a400"},
 };
 
 TheengsDecoder::BLE_ID_NUM test_mfgdata_id_num[]{
@@ -1048,6 +1054,9 @@ TheengsDecoder::BLE_ID_NUM test_mfgdata_id_num[]{
     TheengsDecoder::BLE_ID_NUM::VICTSBS,
     TheengsDecoder::BLE_ID_NUM::VICTSBS,
     TheengsDecoder::BLE_ID_NUM::VICTSBS,
+    TheengsDecoder::BLE_ID_NUM::H5140,
+    TheengsDecoder::BLE_ID_NUM::H5140,
+    TheengsDecoder::BLE_ID_NUM::H5140,
 };
 
 // uuid test input [test name] [device name] [uuid] [manufacturer data] [service data]