Add device classes to binary_sensor for CO and CO2

[epenet]

As I was working on home-assistant/core#61665, I found that device classes CO and CO2 were available on Sensor platform, but not on BinarySensor platform.

CO and CO2 were originally discussed for Sensor platform in #520

I propose that they get added to BinarySensor platform.

[farmio]

Just out of interest: what does a CO2 BinarySensor show?

[emontnemery]

I'm still a bit curious about this. Googling for "CO2 alarm" only gets me results from people who confuse CO2 with CO, are there any binary CO2 detectors on the market and if there are are any integrated with Home Assistant?

CO2 sensors are used to monitor air quality, for example https://www.se.com/ww/en/product/SED-CO2-G-5045/wireless-co2-sensor-with-room-temperature-and-humidity-for-se8000-series-zigbee-communication-protocol/
Maybe there are some which have a binary output to for example increase the ventilation?
Or maybe we want to allow the user to make a template binary CO2 sensor which triggers at some CO2 threshold?

[Jc2k]

This sort of talks about how this works for a homekit device.

https://www.thinka.eu/faq/how-do-i-configure-my-carbon-dioxide-co2-sensor

[Jc2k]

And looking at the HAP spec more closely, a co2 sensor MUST have a binary alert for when dangerous levels are detected. The actual value itself is optional.

[emontnemery]

That link explains that it's possible to map a KNX group address to a homekit CARBON_DIOXIDE_DETECTED characteristic I think.
This KNX CO2 sensor, https://partner.gira.com/en/produkte/gebaeudetechnik/klima-heizungssteuerung/knx-co2sensor.html allows setting up "limiting value" connected to the CO2 values, which could then presumably be configured as a homekit CARBON_DIOXIDE_DETECTED characteristic.

In our case it would probably mean configuring a template binary sensor?

[Jc2k]

That's definitely an option that should be supported, but to be clear we are all on the same page: according to the HAP spec every homekit CO and CO2 sensor will have a Boolean "detected" characteristic, and may not have a integer (ppm) level characteristic.

[epenet]

Draft implementation PR: home-assistant/core#61962
Draft documentation PR: home-assistant/home-assistant.io#20721
Draft frontend PR: home-assistant/frontend#10935

[MartinHjelmare]

What integrations can leverage these device classes?

[emontnemery]

Every CO and CO2 sensor integration technically needs a binary_sensor so that it can be shown in home on iOS (even if a template), as the spec says the binary version is the required value.

We can't burden the integrations or the user with limitations in homekit by making it the integration's or user's responsibility to ensure each CO or CO2 sensor is matched with a corresponding binary sensor though, this probably needs to be handled in the homekit integration itself by binarizing CO or CO2 sensor data if no binary sensor is available in the device?

[bdraco]

Ignoring the HomeKit case for a moment, Home CO detectors are usually binary sensors since they have two states:

0: no CO detected - everything is ok
1: CO detected - risk of CO poisoning - alarm is probably going off

CO2 has much lower risks since you need concentrations of 10% of higher before risking death. Usually this is only going to be some type of binary alarm for a commercial setting, maybe some place that frequently works dry ice such as a vaccination center.

[emontnemery]

Ok, so which integrations providing binary sensor entities would benefit from adding binary sensor device classes?

[epenet]

With covid-19, I think CO2 binary sensors would be used to trigger "this room needs airing" rather than "risk of death"

[bdraco]

Doing a quick product search I find a multitude of CO alarm products that are binary sensors (alarm is on or off, risk of death).

I couldn't find any CO2 alarm products intended for a Home market. Everything I found measured CO2 in PPM

I support a CO binary sensor device class.

I don't see a justification for a CO2 one though as there doesn't seem to be a home market for these.

[emontnemery]

Adding the comment from @bdraco as a concrete proposal: #690 (reply in thread), with integrations supporting CO binary sensors listed here: #690 (reply in thread)

Let's add a CO binary sensor device class.
There's no a justification for a CO2 binary sensor device class at this point as there doesn't seem to be a home market for these.

[MartinHjelmare]

Sounds good!

[epenet]

I have updated the three PRs to only include carbon monoxide.