Summer solstice

I would like a device that simply takes digital audio input and sends it to an AirPlay receiver. How hard can it be?
Instinctively typed “spctl –list” and learned that it’s apparently an undocumented but handy thing, if you’re poking around with spctl often…
Apple Watch unlock on macOS is pretty nice (now that it’s somewhat reliable), but what I’d really like is the reverse: a way to lock the Mac from my watch as I notice an adversary (=my child) is approaching an unlocked computer.