Now I got you. And now I understand what you talked about 
In fact the only thing I changed was to delete the data_template.
That may allow it to pass Check Configuration but, upon execution, errors will be reported in Log.
Try the example I posted above or this reduced version:
- alias: co2_alarm
description: "CO2 - Ampel"
trigger:
- platform: state
entity_id:
- sensor.netatmo_unser_heim_wohnzimmer_buro_co2
- sensor.netatmo_unser_heim_wohnzimmer_kuche_co2
- sensor.netatmo_unser_heim_wohnzimmer_co2
action:
- service: input_text.set_value
target:
entity_id: >-
{% set oid = trigger.to_state.object_id %}
input_text.co2_{{ 'buero' if 'buro' in oid else 'kuche' if 'kueche' in oid else 'wohnzimmer' }}
data:
value: >-
{% set co2 = trigger.to_state.state | int %}
{% set x = 'grün' if co2 <= 800 else 'gelb' if 800 < co2 <= 1000 else 'orange' if 1000 < co2 <= 1400 else 'rot' %}
{{ x }} mit {{ co2 }} ppm
mode: queued
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As sson as possible I‘ll give it a try. I like short code 
Did you have a chance to try it yet?
Indeed, I tried it this afternoon. It works fine. Thank you for that.
Again I learned how to do it in a better way 
Glad to hear it.
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Well, of course 
But what code do I need instead of to_state.object_id?
Is it like this?
trigger:
- platform: zone
entity_id: device_tracker.doris_iphone_2
zone: zone.home_outer_ring
event: enter
action:
- service: input_datetime.set_datetime
target:
entity_id: >-
{% set enter = trigger.zone.object_id %}
input_datetime.doris{{ 'outer' if 'outer' in enter }}
Did you try trigger.to_state.object_id?
I didn‘t. I thought it is zone, so I used zone. Sorry for stupid questions but I am an absolute beginner …
By the way, I didn‘t figure out how to test entering a zone by using the dev. tools 
I tried the following and it didn‘t work. Just the else part is working.
- alias: doris_enter
trigger:
- platform: zone
entity_id: device_tracker.doris_iphone_2
zone: zone.home_outer_ring
event: enter
- platform: zone
entity_id: device_tracker.doris_iphone_2
zone: zone.davids_home_middle_ring
event: enter
- platform: zone
entity_id: device_tracker.doris_iphone_2
zone: zone.home
event: enter
action:
- service: input_datetime.set_datetime
target:
entity_id: >-
{% set oid = trigger.to_state.object_id %}
input_datetime.doris_{{ 'outer' if 'outer' in oid else 'middle' if 'middle' in oid else 'home' }}
data:
datetime: "{{ now().strftime('%Y-%m-%d %H:%M') }}"
mode: single
I don’t have any device_trackers or zones so I can’t test anything for you. In this situation you have three separate triggers so it’s more efficient to simply assign an id to each trigger and use that in the template.
- alias: doris_enter
trigger:
- platform: zone
entity_id: device_tracker.doris_iphone_2
zone: zone.home_outer_ring
event: enter
id: 'outer'
- platform: zone
entity_id: device_tracker.doris_iphone_2
zone: zone.davids_home_middle_ring
event: enter
id: 'middle'
- platform: zone
entity_id: device_tracker.doris_iphone_2
zone: zone.home
event: enter
id: 'home'
action:
- service: input_datetime.set_datetime
target:
entity_id: "input_datetime.doris_{{ trigger.id }}"
data:
datetime: "{{ now().timestamp() | timestamp_local }}"
mode: single
Boah, that easy. Thank you so much!!!
But what is wrong with my datetime?
I posted a different version of the datetime template just to show there’s another way to do the same thing.
I tried the code but unfortunately it doesn‘t work at all. None of the timedate inputs are filled
How did you test the automation? Did device_tracker.doris_iphone_2 move from one zone to another?
Yep. In real life 