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Sensor Entity

A sensor is a read-only entity that provides some information. Information has a value and optionally, a unit of measurement. Derive entity platforms from homeassistant.components.sensor.SensorEntity

Properties

tip

Properties should always only return information from memory and not do I/O (like network requests). Implement update() or async_update() to fetch data.

NameTypeDefaultDescription
device_classstringNoneType of sensor.
last_resetdatetime.datetimeNoneThe time when an accumulating sensor such as an electricity usage meter, gas meter, water meter etc. was initialized. If the time of initialization is unknown, set it to None. Note that the datetime.datetime returned by the last_reset property will be converted to an ISO 8601-formatted string when the entity's state attributes are updated. When changing last_reset, the state must be a valid number.
native_valueNone, datetime.date, datetime.datetime, float, int, stringRequiredThe value of the sensor in the sensor's native_unit_of_measurement. Using a device_class may restrict the types that can be returned by this property.
native_unit_of_measurementstringNoneThe unit of measurement that the sensor's value is expressed in. If the native_unit_of_measurement is °C or °F, and its device_class is temperature, the sensor's unit_of_measurement will be the preferred temperature unit configured by the user and the sensor's state will be the native_value after an optional unit conversion. If not None, the sensor is assumed to be numerical and will be displayed as a line-chart in the frontend instead of as discrete values.
state_classstringNoneType of state. If not None, the sensor is assumed to be numerical and will be displayed as a line-chart in the frontend instead of as discrete values.
tip

Instead of adding extra_state_attributes for a sensor entity, create an additional sensor entity. Attributes that do not change are only saved in the database once. If extra_state_attributes and the sensor value both frequently change, this can quickly increase the size of the database.

Available device classes

If specifying a device class, your sensor entity will need to also return the correct unit of measurement.

TypeSupported unitsDescription
apparent_powerVAApparent power
aqiAir Quality Index
battery%Percentage of battery that is left
carbon_dioxideppmConcentration of carbon dioxide.
carbon_monoxideppmConcentration of carbon monoxide.
currentACurrent
dateDate. Requires native_value to be a Python datetime.date object, or None.
energyWh, kWh, MWhEnergy, statistics will be stored in kWh. Represents power over time. Not to be confused with power.
frequencyHz, kHz, MHz, GHzFrequency
gasm³, ft³Volume of gas, statistics will be stored in m³. Gas consumption measured as energy in kWh instead of a volume should be classified as energy.
humidity%Relative humidity
illuminancelx, lmLight level
monetaryISO 4217Monetary value with a currency.
nitrogen_dioxideµg/m³Concentration of nitrogen dioxide
nitrogen_monoxideµg/m³Concentration of nitrogen monoxide
nitrous_oxideµg/m³Concentration of nitrous oxide
ozoneµg/m³Concentration of ozone
pm1µg/m³Concentration of particulate matter less than 1 micrometer
pm25µg/m³Concentration of particulate matter less than 2.5 micrometers
pm10µg/m³Concentration of particulate matter less than 10 micrometers
powerW, kWPower, statistics will be stored in W.
power_factor%Power Factor
pressurecbar, bar, hPa, inHg, kPa, mbar, Pa, psiPressure, statistics will be stored in Pa.
reactive_powervarReactive power
signal_strengthdB, dBmSignal strength
sulphur_dioxideµg/m³Concentration of sulphure dioxide
temperature°C, °FTemperature, statistics will be stored in °C.
timestampTimestamp. Requires native_value to return a Python datetime.datetime object, with time zone information, or None.
volatile_organic_compoundsµg/m³Concentration of volatile organic compounds
voltageVVoltage

Available state classes

TypeDescription
measurementThe state represents a measurement in present time, not a historical aggregation such as statistics or a prediction of the future. Examples of what should be classified measurement are: current temperature, humidify or electric power. Examples of what should not be classified as measurement: Forecasted temperature for tomorrow, yesterday's energy consumption or anything else that doesn't include the current measurement. For supported sensors, statistics of hourly min, max and average sensor readings is updated every 5 minutes.
totalThe state represents a total amount that can both increase and decrease, e.g. a net energy meter. Statistics of the accumulated growth or decline of the sensor's value since it was first added is updated every 5 minutes. This state class should not be used for sensors where the absolute value is interesting instead of the accumulated growth or decline, for example remaining battery capacity or CPU load; in such cases state class measurement should be used instead.
total_increasingSimilar to total, with the restriction that the state represents a monotonically increasing positive total, e.g. a daily amount of consumed gas, weekly water consumption or lifetime energy consumption. Statistics of the accumulated growth of the sensor's value since it was first added is updated every 5 minutes.

Entity options

Sensors can be configured by the user, this is done by storing sensor entity options in the sensor's entity registry entry.

OptionDescription
unit_of_measurementThe sensor's unit of measurement can be overridden for sensors with device class pressure or temperature.

Restoring sensor states

Sensors which restore the state after restart or reload should not extend RestoreEntity because that does not store the native_value, but instead the state which may have been modifed by the sensor base entity. Sensors which restore the state should extend RestoreSensor and call await self.async_get_last_sensor_data from async_added_to_hass to get access to the stored native_value and native_unit_of_measurement.

Long-term Statistics

Home Assistant has support for storing sensors as long-term statistics if the entity has the right properties. To opt-in for statistics, the sensor must have state_class set to one of the valid state classes: measurement, total or total_increasing. For certain device classes, the unit of the statistics is normalized to for example make it possible to plot several sensors in a single graph.

Entities not representing a total amount

Home Assistant tracks the min, max and mean value during the statistics period. The state_class property must be set to measurement, and the device_class must not be either of energy, gas, or monetary

Entities representing a total amount

Entities tracking a total amount have a value that may optionally reset periodically, like this month's energy consumption, today's energy production or the yearly growth of a stock portfolio. The sensor's value when the first statistics is compiled is used as the initial zero-point.

How to choose state_class and last_reset

It's recommended to use state class total without last_reset whenever possible, state class total_increasing or total with last_reset should only be used when state class total without last_reset does not work for the sensor.

Examples

  • The sensor's value never resets, e.g. a lifetime total energy consumption or production: state_class total, last_reset not set or set to None
  • The sensor's value may reset to 0, and its value can only increase: state class total_increasing. Examples: energy consumption aligned with a billing cycle, e.g. monthly, an energy meter resetting to 0 every time it's disconnected
  • The sensor's value may reset to 0, and its value can both increase and decrease: state class total, last_reset updated when the value resets. Examples: net energy consumption aligned with a billing cycle, e.g. monthly.
  • The sensor's state is reset with every state update, for example a sensor updating every minute with the energy consumption during the past minute: state class total, last_reset updated every state change.

State class total

For sensors with state class total, the last_reset attribute can optionally be set to gain manual control of meter cycles. The sensor's state when it's first added to Home Assistant is used as an initial zero-point. When last_reset changes, the zero-point will be set to 0. If last_reset is not set, the sensor's value when it was first added is used as the zero-point when calculating sum statistics.

To put it in another way: the logic when updating the statistics is to update the sum column with the difference between the current state and the previous state unless last_reset has been changed, in which case don't add anything.

Example of state class total without last_reset:

tstatesumsum_increasesum_decrease
2021-08-01T13:00:001000000
2021-08-01T14:00:00101010100
2021-08-01T15:00:000-1000101010
2021-08-01T16:00:005-995151010

Example of state class total with last_reset:

tstatelast_resetsumsum_increasesum_decrease
2021-08-01T13:00:0010002021-08-01T13:00:00000
2021-08-01T14:00:0010102021-08-01T13:00:0010100
2021-08-01T15:00:0010052021-08-01T13:00:005105
2021-08-01T16:00:0002021-09-01T16:00:005105
2021-08-01T17:00:0052021-09-01T16:00:0010155

Example of state class total where the there initial state at the beginning of the new meter cycle is not 0, but 0 is used as zero-point:

tstatelast_resetsumsum_increasesum_decrease
2021-08-01T13:00:0010002021-08-01T13:00:00000
2021-08-01T14:00:0010102021-08-01T13:00:0010100
2021-08-01T15:00:0010052021-08-01T13:00:005105
2021-08-01T16:00:0052021-09-01T16:00:0010155
2021-08-01T17:00:00102021-09-01T16:00:0015205

State class total_increasing

For sensors with state_class total_increasing, a decreasing value is interpreted as the start of a new meter cycle or the replacement of the meter. It is important that the integration ensures that the value cannot erroneously decrease in the case of calculating a value from a sensor with measurement noise present. There is some tolerance, a decrease between state changes of < 10% will not trigger a new meter cycle. This state class is useful for gas meters, electricity meters, water meters etc. The value when the sensor reading decreases will not be used as zero-point when calculating sum statistics, instead the zero-point will be set to 0.

To put it in another way: the logic when updating the statistics is to update the sum column with the difference between the current state and the previous state unless the difference is negative, in which case don't add anything.

Example of state class total_increasing:

tstatesum
2021-08-01T13:00:0010000
2021-08-01T14:00:00101010
2021-08-01T15:00:00010
2021-08-01T16:00:00515

Example of state class total_increasing where the sensor does not reset to 0:

tstatesum
2021-08-01T13:00:0010000
2021-08-01T14:00:00101010
2021-08-01T15:00:00515
2021-08-01T16:00:001020