cron script to turn your security camera on and off based on the presence of your phone on the wifi

motion-cron.sh

#!/bin/bash

# This assumes you have https://motion-project.github.io/ installed.
# It also assumes this machine is on the same LAN as your phone.
# Put this script in root's crontab; set it to run every minute.
#
# Copyright 2022 <https://doriantaylor.com/person/dorian-taylor#me>
# License Apache-2.0 <https://www.apache.org/licenses/LICENSE-2.0>

# Change this to your phone's mac address
# (and make sure it isn't spoofing while on your network)
MAC=de:ad:be:ef:ca:fe

phone=$(($(/usr/sbin/arp -a | grep -q $MAC && echo 1) + 0))
motion=$(($(ps ho pid -C motion) + 0))

if [[ $motion -gt 0 ]]; then
    if [[ $phone -gt 0 ]]; then
        echo "phone is present on the network; killing motion"
        kill $motion
    fi
elif [[ $phone -le 0 ]]; then
    echo "phone has left the network; starting motion"
    su motion -c motion
fi