I use FHEM (https://fhem.de/ https://fhem.de/) to run a periodic ARP scan for "known" mobile wlan. Once the last one logs off the wlan, FHEM switches secondary

I use FHEM (https://fhem.de/ https://fhem.de/) to run a periodic ARP scan for "known" mobile wlan. Once the last one logs off the wlan, FHEM switches secondary power sources and lights off after 15 minutes. When the devices log back in and there is insufficient natural lighting, it switches the lights back on. Another, unrelated, automation step we implemented is an app checking alarms on our smartphones. When an alarm goes off, FHEM runs a script which switches lights on and reads aloud (with Festival) breaking news, the weather forecast and any interruptions on our daily commute.