Struggling with MQTT - again

It’s probably pretty simple but I just can’t get it sorted out, again:
I’d like to show an icon in my UI that shows the status of my alarm.

This is what I can see in MQTT Explorer:
        friendly_name = "Ready to Arm?"
        icon = "mdi:lock-open-outline"
        last_changed = 2020-08-28T02:21:22.442749+00:00
        last_updated = 2020-08-28T02:21:22.592031+00:00
        state = False

And when ?Ready to Arm?" is True, the icon message changes to “mdi:lock”.

I’m struggling to either show the appropriate lock-icon for the correct state or show the lock in highlighted color when “True” and muted color when 'False" - like a switch would show on and off.

Actually, ideally I would like to show a highlighted lock when true and a muted open lock when false.

It can probably all be done as one sensor/switch/binary_sensor but I just can’t figure out how.

If you currently have your lock state integrated as a binary_sensor, you could just use:

device_class: lock

I have this in my binary_sensor.yaml file:

- platform: mqtt
  name: "Ready to Arm?"
  device_class: lock
  state_topic: "rpi3_info/sensor/ready_to_arm/state"

and it doesn’t show the status change at all, it just stays at ‘off’ = ‘locked’ (which is the wrong way round from my POV to begin with but I could live with that if the status change worked).