Auto-lock your KDE when bluetooth device disconnected

bluetooth-lock.sh

#!/bin/bash

isLocked=false
macaddress=00:00:00:00:00:00

while true; do
        connected=$(bluetoothctl connect $macaddress)
        if [[ $connected == *"org.bluez.Error.Failed"* ]]; then
                if $isLocked; then
                        sleep 5
                else
                        loginctl lock-session
                        isLocked=true
                        sleep 15
                fi
        else 
                isLocked=false
        fi
        sleep 1
done

For this script to work, you will need to have bluetoothctl available and have your device paired.

Change the macaddress variable to your device MAC address