developers.home-assistant/docs/core/entity/sensor.md

title	sidebar_label
Sensor Entity	Sensor

A sensor is a read-only entity that provides some information. Information has a value and optionally, a unit of measurement.

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. :::

Name	Type	Default	Description
state	string	Required	The value of the sensor.
device_class	string	None	Type of sensor.
last_reset	datetime.datetime	None	The 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 and the meter will never reset, set to UNIX epoch 0: homeassistant.util.dt.utc_from_timestamp(0). 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.
state_class	string	None	Type of state.
unit_of_measurement	string	None	The unit of measurement that the sensor is expressed in.

Available device classes

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

Type	Unit	Description
battery	%	% of battery that is left.
carbon_dioxide	ppm	parts per million of carbon dioxide concentration
carbon_monoxide	ppm	parts per million of carbon monoxide concentration
humidity	%	% of humidity in the air.
illuminance	lx/lm	Light level.
signal_strength	dB/dBm	Signal strength.
temperature	°C/°F	Temperature.
timestamp	ISO8601	Timestamp.
power	W,kW	Power.
pressure	hPa,mbar	Pressure.
current	A	Current.
energy	Wh,kWh	Energy.
power_factor	%	Power Factor.
voltage	V	Voltage.
monetary	ISO 4217	Monetary value with a currency

Available state classes

Type

Description

measurement

The 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, accumulated energy consumption, accumulated cost. Exampled 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.