---
- platform: template
  sensors:
    number_windows_open:
      friendly_name: "Windows Open"
      unit_of_measurement: window(s)
      value_template: >
        {{ states.binary_sensor | selectattr('object_id', 'match', 'window_.*') | selectattr('state', '==', 'on') | map(attribute='entity_id') | list | count }}