Sensors are a basic platform component in Home Assistant. They monitor the states and conditions of a variety of entities. An entity can be many things. This can include a physical device like a motion sensor that reports the battery level, a web service that retrieves the weather temperature, a built-in function that calculates the sun’s elevation relative to your GPS position, or even a custom sensor you may have created to report the free space on your laptop. These are all things reporting different types of information.
Some of these sensors are built-in to Home Assistant, some are created automatically when you add an integration (see this list), and some can be created manually. The Statistics and Template sensors are two examples of the last case.
The type of data a sensor returns impacts how it is displayed in the frontend. This is controlled by the sensor’s device class designation. Built-in sensors and many created from an integration will have this designation predefined. Those can be modified in the customize section. When manually creating a new sensor the device class may be optionally assigned. A full list of available sensor device classes is below:
- None: Generic sensor. This is the default and doesn’t need to be set.
- aqi: Air Quality Index
- battery: Percentage of battery that is left.
- carbon_dioxide: Carbon Dioxide in CO2 (Smoke)
- carbon_monoxide: Carbon Monoxide in CO (Gas CNG/LPG)
- current: Current in A.
- date: Date string (ISO 8601).
- energy: Energy in Wh, kWh or MWh.
- frequency: Frequency in Hz, kHz, MHz or GHz.
- gas: Gasvolume in m³ or ft³.
- humidity: Percentage of humidity in the air.
- illuminance: The current light level in lx or lm.
- monetary: The monetary value.
- nitrogen_dioxide: Concentration of Nitrogen Dioxide in µg/m³
- nitrogen_monoxide: Concentration of Nitrogen Monoxide in µg/m³
- nitrous_oxide: Concentration of Nitrous Oxide in µg/m³
- ozone: Concentration of Ozone in µg/m³
- pm1: Concentration of particulate matter less than 1 micrometer in µg/m³
- pm10: Concentration of particulate matter less than 10 micrometers in µg/m³
- pm25: Concentration of particulate matter less than 2.5 micrometers in µg/m³
- power_factor: Power factor in %.
- power: Power in W or kW.
- pressure: Pressure in hPa or mbar.
- signal_strength: Signal strength in dB or dBm.
- sulphur_dioxide: Concentration of sulphur dioxide in µg/m³
- temperature: Temperature in °C or °F.
- timestamp: Datetime object or timestamp string (ISO 8601).
- volatile_organic_compounds: Concentration of volatile organic compounds in µg/m³.
- voltage: Voltage in V.
Example of various device class icons for sensors.