Script to observe for smartwatch's BT signal strength and autolock when it's weak

watch-autolock.sh

#!/usr/bin/env nix-shell
#!nix-shell -i bash -p bluez

BT_DEVICE="XX:XX:XX:XX:XX:XX"
BT_RSSI_THRESHOLD=-15

get_rssi() {
	out=$(hcitool rssi $BT_DEVICE) || return 1
	out=${out#*: }
	echo $out
}

rssi_is_within_threshold() {
	local rssi="$1"
	(( rssi >= BT_RSSI_THRESHOLD ))
}

screen_is_locked() {
	out=$(dbus-send \
		--session --print-reply=literal \
		--dest=org.gnome.ScreenSaver \
		/org/gnome/ScreenSaver \
		org.gnome.ScreenSaver.GetActive)
	[[ $out == *true* ]]
}

lock_screen() {
	dbus-send \
		--type=method_call \
		--dest=org.gnome.ScreenSaver \
		/org/gnome/ScreenSaver \
		org.gnome.ScreenSaver.Lock
}

main() {
	while true; do
		if screen_is_locked; then
			echo "Screen is already locked, see you in a minute!"
			sleep 1m
			continue
		fi

		if ! rssi=$(get_rssi); then
			echo "Device not connected, not doing anything..."
			sleep 1s
			continue
		fi

		if rssi_is_within_threshold $rssi; then
			echo "Device is within range, continuing..."
			sleep 1s
			continue
		fi

		echo "Device is out of range, locking screen!"
		lock_screen
		sleep 5s
	done
}

main

Device will need to be paired with the computer first.