Do I need a value template to create a low battery automation?

[itm1960]

I would like to create automations to alert me when the battery level of certain devices falls below a specified level. I have put together the following:

alias: Battery Low - front door sensor
description: ''
trigger:
  - platform: state
    entity_id: sensor.ewelink_ds01_a670ff22_power
    to: <10
    for: '500'
condition: []
action:
  - service: notify.mobile_app_moto_g_5g_plus
    data:
      title: Alarm sensor battery low
      message: Front Door sensor battery is low
mode: single

…but when I search for examples of battery level alerts I usually see value templates used. Since I don’t know anything about value templates I’d prefer to keep things simple (like the above).
Could anyone advise:

• would my code above work OK?
• why I might consider using a value template?

[ardysusilo (Ardy)]

@itm1960

would my code above work OK?

No, it won’t work. Instead, use Numeric State Trigger-

trigger:
  - platform: numeric_state
    entity_id: sensor.ewelink_ds01_a670ff22_power
    below: '10'
    for: '00:08:20'

[Jonah1970 (Mark)]

You can find many battery alert solutions on the forums and these often work without the need to define templates or triggers for every battery sensor meaning that any new sensors you add get included automatically.

This is the one I have been using:

Automation Trigger: list of devices

Please explain how that’s possible. Where are the identifiable entities within the binary_sensor’s template? PS I tested the suggested binary_sensor, using three MQTT Sensors reporting battery level. Publishing a payload value of less than 50 to their state_topic results in no state change for the binary_sensor. That’s an expected result because the binary_sensor’s template contains no identifiable entities (so no listeners can be created to monitor the binary_sensor).

[itm1960]

Thanks for the example. I have 2 questions:

1. Will the numeric state trigger work if the value is a string (which it appears to be)
2. Was a particular reason for choosing ‘00:08:20’ for the “for” value?

[ardysusilo (Ardy)]

@itm1960

Will the numeric state trigger work if the value is a string (which it appears to be)

Yes it will. Follow the example in the documentation on how to write it properly.

@itm1960

Was a particular reason for choosing ‘00:08:20’ for the “for” value?

It simply converts your 500 seconds to minutes and seconds.