HAOS on laptop, detecting AC loss

I installed HAOS on an old Microsoft Surface Laptop and it is running fine. Is it possible to detect when the laptop switches to running on battery power due to AC loss, and run some automation when this occurs and when AC is restored?

You should be able to do it with a hass agent sensor:

Thanks. I read through the Readme and it seems it’s intended as a windows client. I’m running HAOS, which I thought is Linux-based, so am I still able to use this agent?

This seems relevant


Doh. Yeah. Sorry.

This kind of info is usually found in /proc or /sys somewhere.

Once you have found out where, you should be able to use a commandline sensor.

I do this, but I run HA core. Perhaps this might help. I believe HAOS is Debian-based.

I have a udev rule:

SUBSYSTEM=="power_supply",ENV{POWER_SUPPLY_NAME}=="AC0",RUN+="/usr/bin/curl -s -X POST http://localhost:8123/api/webhook/server_power_connected -d 'status=$env{POWER_SUPPLY_ONLINE}'"

And my automation:

# udevadm monitor
# udevadm info --path=/sys/class/power_supply/AC0
# /etc/udev/rules.d/60-power.rules
# SUBSYSTEM=="power_supply",ENV{POWER_SUPPLY_NAME}=="AC0",RUN+="/usr/bin/curl -s -X POST http://<host>:<port>/api/webhook/<webhook_id> -d 'status=$env{POWER_SUPPLY_ONLINE}'"
# udevadm control --reload-rules && udevadm trigger
# sudo /etc/init.d/udev restart
# udevadm control --log-priority=debug
# (sudo) journalctl -f
- alias: "Update Server Power Status"
  initial_state: true
    - platform: webhook
      webhook_id: server_power_connected
      local_only: true
  mode: queued
    # sensor definition: platform: linux_battery
    - service: homeassistant.update_entity
      entity_id: sensor.home_assistant_server_battery


- platform: linux_battery
  name: Home Assistant Server Battery
  battery: 0
  system: linux
  scan_interval: 60


      friendly_name: "Electricity"
      # https://www.home-assistant.io/integrations/binary_sensor/#device-class
      device_class: power
      value_template: >-
        {{ not is_state_attr('sensor.home_assistant_server_battery', 'status', 'Discharging') }}
      icon_template: >-
        {% if is_state_attr('sensor.home_assistant_server_battery', 'status', 'Discharging') %}
        {% else %}
        {% endif %}

Specifically, on my Lenovo Thinkpad (so the power hardware will be different, so your details may vary) reading /sys/class/power_supply/AC/online gives me 0 when on battery and 1 when power is pugged in.

No. Based on buildroot.

Thanks Nick.

EDIT: Not familiar with the tool, but a quick search shows that udev is supported.