Sensor

The sensor accessor returns read-only Sensor entities — anything HA reports a value for: temperature, humidity, power, presence counts, energy totals, and so on.

Reading values

sensor = ha.sensor("outdoor_temperature")

print(sensor.value)                  # float, str, or None
print(sensor.unit_of_measurement)    # "°C", "kWh", "%", ...
print(sensor.device_class)           # "temperature", "energy", ...
print(sensor.state)                  # the raw HA state string
print(sensor.attributes)             # full attribute dict

value is HaClient's normalised view of the sensor reading:

• If the state parses as a number, you get a float.
• If it does not, you get the raw state string (e.g. "on", "home").
• If the entity is unavailable or has not arrived yet, you get None.

For absolute fidelity, read sensor.state (always a string) and sensor.attributes directly.

Reacting to changes

@sensor.on_value_change
def changed(old, new):
    print(f"{sensor.entity_id}: {old} -> {new}")

on_value_change fires on any state-string change. The handler receives the raw old/new strings; if you want the normalised numeric value, read sensor.value inside the handler.

Common patterns

Threshold alerting

@sensor.on_value_change
async def temp_alert(old, new):
    v = sensor.value
    if isinstance(v, float) and v > 30.0:
        await notify(f"{sensor.entity_id} is hot: {v} {sensor.unit_of_measurement}")

Periodic polling fallback

State arrives via the event stream, so polling is rarely needed. When you suspect a stale reading after a reconnect or HA restart, force a single refresh:

await sensor.async_refresh()

Or refresh everything at once via await ha.state.refresh_all().

Collecting all sensors in a domain

for entity in ha.sensor.all():
    print(entity.entity_id, entity.value)

all() returns every sensor entity the client has registered so far. Entities are created lazily when you first ask for them by name, so all() only reflects sensors you (or built-in priming) have touched — it is not a discovery API.