Having several ESPhome nodes with sensors, I wanted to use HA to notify me when sensor values er increased. This is especially useful for values which cannot be automated and require human intervention (e.g. CO2, PM2.5/PM10 for ventilation or in worst case evacuation ;)).
Thanks for help to @finity, @123 and @pedolsky for help 
(see here and here).
Goal
- Get notification of any sensor above configurable threshold
- Get regular reminder of high value
- Get reminder when sensor is below configured threshold again
Example
Example of automation trigger with 1000ppm high and 900ppm safe level
Blueprint
Implementation
The blueprint allows selection of the sensor to watch, and high and safe thresholds. The automation is triggered when the sensor crosses the high threshold (numeric_state on trigger_level_high). Until the sensor is below the safe threshold (via wait_for_trigger with numeric_state on trigger_level_low), an hourly notification is sent. With each notification the actual sensor value is sent.
Source
blueprint:
name: High sensor value notification
description: Notify users of high sensor values (e.g. CO2, temp, PM2.5), and again when value drops below acceptable level
domain: automation
input:
trigger_sensor:
name: Trigger sensor
description: E.g. CO2, PM2.5, temperature
selector:
entity:
domain: sensor
trigger_level_high:
name: Trigger level high
description: Notify above this level
selector:
number:
mode: box
min: -50
max: 1250
trigger_level_low:
name: Trigger level low
description: Notify again below this level
selector:
number:
mode: box
min: -50
max: 1250
alias: High sensor value notification+
description: Notify when high sensor values are detected somewhere
trigger:
- platform: numeric_state
entity_id: !input "trigger_sensor"
above: !input "trigger_level_high"
variables:
trigger_sensor_var: !input "trigger_sensor"
trigger_level_high_var: !input "trigger_level_high"
trigger_level_low_var: !input "trigger_level_low"
condition: []
action:
- repeat:
until:
- condition: numeric_state
entity_id: !input "trigger_sensor"
below: !input 'trigger_level_low'
sequence:
- service: notify.notify
data:
message: >-
High reading of {{state_attr(trigger_sensor_var, 'friendly_name')}}
at {{ states(trigger_sensor_var) }}{{state_attr(trigger_sensor_var, 'unit_of_measurement') }}
- wait_for_trigger:
- platform: numeric_state
entity_id: !input "trigger_sensor"
below: !input 'trigger_level_low'
timeout:
minutes: 60
continue_on_timeout: false
- service: notify.notify
data:
message: >-
Reading of {{state_attr(trigger_sensor_var, 'friendly_name')}} back to normal
at {{ states(trigger_sensor_var) }}{{state_attr(trigger_sensor_var, 'unit_of_measurement') }}
mode: single