# Netatmo CO2 reading from multipe indoor units **URL:** \ **Category:** Questions & Help\ **Created:** [January 12, 2021, 12:33pm UTC](https://community.homey.app/t/netatmo-co2-reading-from-multipe-indoor-units/40964 "2021-01-12T12:33:38Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![lebetten](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/lebetten/32/31499_2.png) [@lebetten](https://community.homey.app/u/lebetten)\ **Post date:** [January 12, 2021, 12:33pm UTC](https://community.homey.app/t/netatmo-co2-reading-from-multipe-indoor-units/40964/1 "2021-01-12T12:33:38Z")
I’m controlling my ventilation system (systemair) from homey, and the controll works like a sharm. I want to controll the strength of the ventilation on how high the CO2 level is in a room. It has not been a problem setting up some flows for one sensor. But my problem is to set up a flow for multiple sensors. If I have multiple roules for different rooms. And the livingroom has CO2 level that sets the ventilation to medium, and a bedroom has low CO2 level the ventilation is then set back to low again, because it’s reading the value for the bedroom. Is there a way to gather all my four sensors to one virtual device that always shows the highest value of all devices, that I can use in a flow for the ventilation? ---
**Author:** ![Edwin\_D](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/edwin_d/32/136417_2.png) [@Edwin\_D](https://community.homey.app/u/Edwin_D)\ **Post date:** [January 12, 2021, 3:44pm UTC](https://community.homey.app/t/netatmo-co2-reading-from-multipe-indoor-units/40964/2 "2021-01-12T15:44:44Z")
The group app can do that for you, in the configuration settings for the app you can define the behavior for each value of each group. ---
**Author:** ![lebetten](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/lebetten/32/31499_2.png) [@lebetten](https://community.homey.app/u/lebetten)\ **Post date:** [January 12, 2021, 4:45pm UTC](https://community.homey.app/t/netatmo-co2-reading-from-multipe-indoor-units/40964/3 "2021-01-12T16:45:03Z")
That worked perfectly, thank you ---
**Author:** ![Edwin\_D](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/edwin_d/32/136417_2.png) [@Edwin\_D](https://community.homey.app/u/Edwin_D)\ **Post date:** [January 12, 2021, 5:00pm UTC](https://community.homey.app/t/netatmo-co2-reading-from-multipe-indoor-units/40964/4 "2021-01-12T17:00:55Z")
Pointing to it is easy, thanks forwarded to @Jamie for creating this useful app 🙂