I know I can do this
trigger:
- platform: state
entity_id: vacuum.landroid_chugger
attribute: rain_sensor
But what if my attribute is
rain_sensor:
delay: 60
triggered: false
remaining: 40
and I want to trigger on remaining?
I’ve tried this but it doesn’t seem to work
trigger:
- platform: state
entity_id: vacuum.landroid_chugger
attribute: rain_sensor.remaining
Use a template trigger. The template needs to result in true to trigger, so something like:
platform: template
value_template: "{{ state_attr('sensor.rain_sensor','remaining')|int < 40 }}"
You can check it works properly in Dev Tools > Template first
edit: You may for may not need the |int
I wasn’t clear, sorry.
The attribute is
rain_sensor:
delay: 60
triggered: false
remaining: 40
rain_senor is an attribute, remaining is an attribute of the attribute rain_sensor
Like this,
vacuum.landroid
attribute1: some_value1
attribute2: some_value2
rain_sensor:
delay: 60
triggered: false
remaining: 40
attribute3: some_value3well, OK then 
try this:
platform: template
{% if state_attr('vacuum.landroid','rain_sensor').remaining <40 %} true {% endif %}"
But I don’t want to check on a specific value, I just want to trigger when it changes to anything.
Why is your initial try not doing what you want then?
Will delay or triggered change while remaining would be the same? Would it actually matter?
It appears that a change to child-attributes does not trigger a change to the parent.
It would in this case
vacuum.landroid
attribute1: some_value1
attribute2: some_value2
rain_sensor: some_value
delay: 60
triggered: false
remaining: 40
attribute3: some_value3
but in this case rain_sensor itself has no value to change.
And in any case I still want to know if the child-attribute changes. All the children change independently for different reasons.
Just so you know what I mean, remaining starts at 60 (the value of delay) and decreases with time until it reaches zero. Unless or until it goes back to 60 when triggered becomes true again.
What do you mean by “child attribute”?
Please show a screenshot of the state of your entities in the developer tools, because the way you show it doesn’t make sense in HA: attributes have only 1 “level”.
So the attributes of the “vacuum.landroid” entity might look similar to
attribute1: some_value1
attribute2: some_value2
rain_sensor: "{delay: 60, triggered: false, remaining: 40}"
attribute3: some_value3
Random example:
put this into Dev tools > template
{{ state_attr('vacuum.landroid','rain_sensor') }}
I think you might need to add a helper to hold the last value of the attribute and then use a template trigger to run the actions when the new attribute is not equal to the old attribute value:
trigger:
- platform: template
value_template: "{{ state_attr('vacuum.landroid_chugger', 'rain_sensor').remaining != states('input_text.some_entity') }}"
action:
- service: input_text.set_value
entity_id: inout_text.some_entity
data:
value: "{{ state_attr('vacuum.landroid_chugger', 'rain_sensor').remaining }}"
- some other actions
To get the value, you would use:
{{ state_attr('vacuum.landroid','rain_sensor')[0].remaining }}
My pure guess … I would believe that you could use a template trigger on the attribute ‘rain_sensor’ and trigger variables trigger.from_state and trigger.to_state to evaluate whether the change was in the remaining. Then use that variable boolean to do nothing or do something in the automation.
Never saw that before. Which integration is this?
EDIT: I guess
I’m pretty sure that what they do with objects in attributes is unsupported
Your most reliable option is to set up a template sensor to monitor the sub-attribute, then you can use a basic State trigger.
template:
- sensor:
- name: Landroid Remaining Rain Delay
unit_of_measurement: minutes
state: "{{ state_attr('vacuum.landroid','rain_sensor')[0].remaining }}"
The other option is to do as @kbrown01 suggested:
trigger:
- platform: state
entity_id: vacuum.landroid
condition:
- condition: template
value_template: |-
{{ (trigger.to_state.attributes.rain_sensor)[0].remaining != (trigger.from_state.attributes.rain_sensor)[0].remaining}}
action:
.....
EDIT: As pointed out below, the [0] index selection may not be necessary, but I do not use the device or integration in question and I am unable to test its necessity. Try it without first, and if you get errors try it with the index selection.
Most of the weather integrations that offer forecasts use something similar…
Why [0]? It’s not an array.
If {{ state_attr('vacuum.landroid','rain_sensor').remaining }} works in the developers tool, then indeed a template is the way to go.
Have you considered making a Template Sensor for it and using that in a State Trigger?
template:
- sensor:
- name: Remaining
state: "{{ state_attr('vacuum.landroid','rain_sensor').remaining }}"
Ah, indeed, I never realized. I stand corrected.
Still, your [0] is wrong, though 
I could only find 1 entity in my instance that is similar to OP’s with just a single set of sub-attributes instead of an explicit array like the weather forecasts and it throws an error (UndefinedError: 'homeassistant.helpers.template.Wrapper object' has no attribute 'today') if I don’t use [0]… 
That’s because it’s an array, as can be seen in the dev tools.
If the “children” start with an hyphen, it’s an array, and then [<index>] is required, indeed.
But that’s not the case for the OP, as can be seen from his screenshot.
The States tool doesn’t always show a hyphen for arrays. (See any thread regarding the mobile app’s Bluetooth Connection sensor and its connected_paired_devices and paired_devices attributes)