[scd4x] Fix ambient_pressure_compensation unit handling (#19888)

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
Co-authored-by: J. Nick Koston <nick@home-assistant.io>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

esphome/components/scd4x/sensor.py

@@ -42,6 +42,15 @@ MEASUREMENT_MODE_OPTIONS = MeasurementMode.options(
 )
 
 
+def pressure_hpa(value: str | float) -> float:
+    """Pressure in hPa. A bare number is hPa, matching what the C++ sends to the sensor."""
+    try:
+        return cv.float_(value)
+    except cv.Invalid:
+        pass
+    return cv.pressure(value) * 1000  # bar, mbar, mBar
+
+
 CONFIG_SCHEMA = (
     cv.Schema(
         {
@@ -72,7 +81,9 @@ CONFIG_SCHEMA = (
                 cv.float_with_unit("altitude", "(m|m a.s.l.|MAMSL|MASL)"),
                 cv.int_range(min=0, max=0xFFFF, max_included=False),
             ),
-            cv.Optional(CONF_AMBIENT_PRESSURE_COMPENSATION): cv.pressure,
+            cv.Optional(CONF_AMBIENT_PRESSURE_COMPENSATION): cv.All(
+                pressure_hpa, cv.Any(cv.float_range(min=700, max=1200), 0)
+            ),
             cv.Optional(CONF_TEMPERATURE_OFFSET, default="4°C"): cv.temperature_delta,
             cv.Optional(CONF_AMBIENT_PRESSURE_COMPENSATION_SOURCE): cv.use_id(
                 sensor.Sensor

tests/components/scd4x/common.yaml

@@ -14,3 +14,19 @@ sensor:
     ambient_pressure_compensation: 961mBar
     temperature_offset: 4.2C
     update_interval: 15s
+  - platform: scd4x
+    i2c_id: i2c_bus
+    co2:
+      name: SCD4X CO2 (bare hPa)
+    ambient_pressure_compensation: 961
+  - platform: scd4x
+    i2c_id: i2c_bus
+    co2:
+      name: SCD4X CO2 (bar)
+    ambient_pressure_compensation: 0.961bar
+  - platform: scd4x
+    i2c_id: i2c_bus
+    co2:
+      name: SCD4X CO2 (altitude only)
+    altitude_compensation: 500m
+    ambient_pressure_compensation: 0