My wife insists on turning the TV off with the TV remote, not the Siri remote. I assume Channels stays running in the background. Anyhow, when she picks up the Siri remote to turn the TV on again it doesn’t work… she has to use the TV remote.
Is there a “HDMI screen powered off” type CEC event Channels can use to stop running when the TV is turned off ?
This is a known issue when you turn off the TV and the app is still running.
We have a radar open with Apple asking about ways to detect when this happens, but never heard anything back. I can try asking again since it’s been a while.
My simple solution. Hide the TV Remote 
Simple LOL!
Or better: get a programmable universal remote, but reprogram the buttons so that the “power off” for the “tv” is a sequence that will power off the ATV then the tv. THEN you can “lose” the tv remote… (I do this anyways so that the “real” remote does not get damaged in case I later on need to use a learning remote without paying outrageous prices on ebay for a replacement since tvs tend to last MUCH longer than the remotes do around here)
In my case we only have the Apple TV Connected to all 8 TV’s. We like to keep it simple to just the one Apple TV Remote. Hard to mess up with you only have 1 remote. I actually do hide the TV Remote.
I also only use the ATV remote. It powers on/off the tv, sound system, and atv instantly. Can be pointed anywhere and works instantly to control all media and sound volume. No crazy buttons for my wife to ask me about. It is way better than a Harmony remote. With Channels on the atv, everything i would use a tv for is covered. all tv shows, dvr recordings, and media from other apps are accessible. Hdmi-cec is great.
Having more gadgets than I care to think about, after having a Siri remote that does everything I need to do, replacing that with something that has “moar buttons !” fills me with dread. Apparently I’ve become one of those minimalists.
Got an update on our radar:
Re: Bug ID 24245764: Add method/notification to detect if television has been turned off
Engineering has determined that your bug report (24245764) is a duplicate of 32598187 and will be closed
Usually this is a good sign, but unfortunately we have no access to the other bug report and can no longer monitor the status of this request.
Strange way to do things. Oh well, thanks for taking a look into it.