From bc28c8fd3c92597ec351324d08f45bcad374cb5e Mon Sep 17 00:00:00 2001
From: Thomas55555 <59625598+Thomas55555@users.noreply.github.com>
Date: Tue, 20 Jan 2026 16:07:24 +0100
Subject: [PATCH] Add ppb as a valid uom for sensor/number CO device class
 (#159554)

---
 homeassistant/components/number/const.py |  3 +-
 homeassistant/components/sensor/const.py |  3 +-
 homeassistant/util/unit_conversion.py    |  2 +
 tests/util/test_unit_conversion.py       | 65 +++++++++++++++++++-----
 4 files changed, 57 insertions(+), 16 deletions(-)

diff --git a/homeassistant/components/number/const.py b/homeassistant/components/number/const.py
index 41b4863cf32..a7f8e80ca97 100644
--- a/homeassistant/components/number/const.py
+++ b/homeassistant/components/number/const.py
@@ -125,7 +125,7 @@ class NumberDeviceClass(StrEnum):
     CO = "carbon_monoxide"
     """Carbon Monoxide gas concentration.
 
-    Unit of measurement: `ppm` (parts per million), `mg/m³`, `μg/m³`
+    Unit of measurement: `ppb` (parts per billion), `ppm` (parts per million), `mg/m³`, `μg/m³`
     """
 
     CO2 = "carbon_dioxide"
@@ -483,6 +483,7 @@ DEVICE_CLASS_UNITS: dict[NumberDeviceClass, set[type[StrEnum] | str | None]] = {
     NumberDeviceClass.BATTERY: {PERCENTAGE},
     NumberDeviceClass.BLOOD_GLUCOSE_CONCENTRATION: set(UnitOfBloodGlucoseConcentration),
     NumberDeviceClass.CO: {
+        CONCENTRATION_PARTS_PER_BILLION,
         CONCENTRATION_PARTS_PER_MILLION,
         CONCENTRATION_MILLIGRAMS_PER_CUBIC_METER,
         CONCENTRATION_MICROGRAMS_PER_CUBIC_METER,
diff --git a/homeassistant/components/sensor/const.py b/homeassistant/components/sensor/const.py
index f223755c061..1702a981c10 100644
--- a/homeassistant/components/sensor/const.py
+++ b/homeassistant/components/sensor/const.py
@@ -159,7 +159,7 @@ class SensorDeviceClass(StrEnum):
     CO = "carbon_monoxide"
     """Carbon Monoxide gas concentration.
 
-    Unit of measurement: `ppm` (parts per million), `mg/m³`, `μg/m³`
+    Unit of measurement: `ppb` (parts per billion), `ppm` (parts per million), `mg/m³`, `μg/m³`
     """
 
     CO2 = "carbon_dioxide"
@@ -597,6 +597,7 @@ DEVICE_CLASS_UNITS: dict[SensorDeviceClass, set[type[StrEnum] | str | None]] = {
     SensorDeviceClass.BATTERY: {PERCENTAGE},
     SensorDeviceClass.BLOOD_GLUCOSE_CONCENTRATION: set(UnitOfBloodGlucoseConcentration),
     SensorDeviceClass.CO: {
+        CONCENTRATION_PARTS_PER_BILLION,
         CONCENTRATION_PARTS_PER_MILLION,
         CONCENTRATION_MILLIGRAMS_PER_CUBIC_METER,
         CONCENTRATION_MICROGRAMS_PER_CUBIC_METER,
diff --git a/homeassistant/util/unit_conversion.py b/homeassistant/util/unit_conversion.py
index 64e3ed9131b..5926a57cd67 100644
--- a/homeassistant/util/unit_conversion.py
+++ b/homeassistant/util/unit_conversion.py
@@ -194,6 +194,7 @@ class CarbonMonoxideConcentrationConverter(BaseUnitConverter):
 
     UNIT_CLASS = "carbon_monoxide"
     _UNIT_CONVERSION: dict[str | None, float] = {
+        CONCENTRATION_PARTS_PER_BILLION: 1e9,
         CONCENTRATION_PARTS_PER_MILLION: 1e6,
         CONCENTRATION_MILLIGRAMS_PER_CUBIC_METER: (
             _CARBON_MONOXIDE_MOLAR_MASS / _AMBIENT_IDEAL_GAS_MOLAR_VOLUME * 1e3
@@ -203,6 +204,7 @@ class CarbonMonoxideConcentrationConverter(BaseUnitConverter):
         ),
     }
     VALID_UNITS = {
+        CONCENTRATION_PARTS_PER_BILLION,
         CONCENTRATION_PARTS_PER_MILLION,
         CONCENTRATION_MILLIGRAMS_PER_CUBIC_METER,
         CONCENTRATION_MICROGRAMS_PER_CUBIC_METER,
diff --git a/tests/util/test_unit_conversion.py b/tests/util/test_unit_conversion.py
index aebcf76744c..e37237a48cb 100644
--- a/tests/util/test_unit_conversion.py
+++ b/tests/util/test_unit_conversion.py
@@ -302,7 +302,32 @@ _CONVERTED_VALUE: dict[
         ),
     ],
     CarbonMonoxideConcentrationConverter: [
+        # PPB to other units
+        (
+            1,
+            CONCENTRATION_PARTS_PER_BILLION,
+            0.001,
+            CONCENTRATION_PARTS_PER_MILLION,
+        ),
+        (
+            1,
+            CONCENTRATION_PARTS_PER_BILLION,
+            1.16441,
+            CONCENTRATION_MICROGRAMS_PER_CUBIC_METER,
+        ),
+        (
+            1,
+            CONCENTRATION_PARTS_PER_BILLION,
+            0.00116441,
+            CONCENTRATION_MILLIGRAMS_PER_CUBIC_METER,
+        ),
         # PPM to other units
+        (
+            1,
+            CONCENTRATION_PARTS_PER_MILLION,
+            1000,
+            CONCENTRATION_PARTS_PER_BILLION,
+        ),
         (
             1,
             CONCENTRATION_PARTS_PER_MILLION,
@@ -315,24 +340,17 @@ _CONVERTED_VALUE: dict[
             1164.41,
             CONCENTRATION_MICROGRAMS_PER_CUBIC_METER,
         ),
-        # MILLIGRAMS_PER_CUBIC_METER to other units
-        (
-            120,
-            CONCENTRATION_MILLIGRAMS_PER_CUBIC_METER,
-            103.05655,
-            CONCENTRATION_PARTS_PER_MILLION,
-        ),
-        (
-            120,
-            CONCENTRATION_MILLIGRAMS_PER_CUBIC_METER,
-            120000,
-            CONCENTRATION_MICROGRAMS_PER_CUBIC_METER,
-        ),
         # MICROGRAMS_PER_CUBIC_METER to other units
         (
             120000,
             CONCENTRATION_MICROGRAMS_PER_CUBIC_METER,
-            103.05655,
+            103056.5,
+            CONCENTRATION_PARTS_PER_BILLION,
+        ),
+        (
+            120000,
+            CONCENTRATION_MICROGRAMS_PER_CUBIC_METER,
+            103.0565,
             CONCENTRATION_PARTS_PER_MILLION,
         ),
         (
@@ -341,6 +359,25 @@ _CONVERTED_VALUE: dict[
             120,
             CONCENTRATION_MILLIGRAMS_PER_CUBIC_METER,
         ),
+        # MILLIGRAMS_PER_CUBIC_METER to other units
+        (
+            120,
+            CONCENTRATION_MILLIGRAMS_PER_CUBIC_METER,
+            103056.5,
+            CONCENTRATION_PARTS_PER_BILLION,
+        ),
+        (
+            120,
+            CONCENTRATION_MILLIGRAMS_PER_CUBIC_METER,
+            103.0565,
+            CONCENTRATION_PARTS_PER_MILLION,
+        ),
+        (
+            120,
+            CONCENTRATION_MILLIGRAMS_PER_CUBIC_METER,
+            120000,
+            CONCENTRATION_MICROGRAMS_PER_CUBIC_METER,
+        ),
     ],
     ConductivityConverter: [
         (