If humidity is lower outside than inside then alert

Configuration
1

I have humidity sensors both inside and out. Is it possible to get an alert to tell me when the humidity outside is lower than inside?

When the weather is drier outside, I’d like to know, to open a window.

Thank you.

2

Yes. You need a Numeric State Trigger for an Automation.

There is even an example how to compare two numeric sensor states to each other:

automation:
  trigger:
    - platform: numeric_state
      entity_id: sensor.inside_humidity
      above: sensor.outside_humidity
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3

Are you aware of relative and absolute humidity?

e.g.:

  • Outside temp < Inside temp, Outside rel. humidity > Inside rel. humidity → Does not mean always that you should not open the window because lower temp air can not hold as much humidity as higher temp air and the relative is only 0-100 % depending on the temperature.

You should calculate the absolute humidity first:
See for example

After that you can compare the absolute humidity inside and outside which are the relevant values to compare.

You can create a binary template sensor for comparing the values and store the “should open window” flag:

You can use the comparison directly in an automation but IMHO, I would store this information in a new template sensor. This makes the trigger easier and you have the data at your history of sensor data.

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