EvilleBill

I set up this exact automation with my home camera* with one additional automation for a little extra peace of mind.  The additional automation is triggered by the outlet turning ON/OFF (not the comings and goings of the HomeKit users).  When the outlet turns on, the automation turns the nightlight on the iDevices switch ON and Red (like the "recording light" of a camera).  Then when the outlet turns off, the automation turns the nightlight to green for 30 minutes before turning off.  This lets me know the camera did record while I/we were 'away', but is not recording currently.  This works like a champ for me.

Cascading HomeKit automations like this can provide a new layer of possibilities.  I intend to experiment with using this concept to control various HomeKit lights around the house to turn on/off at intervals to mimic an occupied home.

* My camera is a Withings "Home", not HomeKit capable.  (Another manufacturing HomeKit compatibility promise broken.  Nokia bought Withings and at the time Nokia was feuding with Apple over licensing, that put the kibosh on that plan to make "Home" HomeKit-able.)  

Hoping that Withings revives its project to add HomeKit compatibility to their Home camera as originally planned before Nokia killed it.