Plex Alexa skill combined with PlexPlus ST app is quite impressive.
Plex recently released a webhook feature so this Plex to ST control works instantly now.
My setup is like this in my living room:
Samsung TV
Nvidia Shield TV (Android TV)
ST connected lights
PlexPlus ST app
Amazon Echo with Plex Skill
One example:
Lights are ON in the living room and TV is OFF
I say “Alexa play movie star trek beyond using plex”
TV turns ON and movie starts and Lights turn OFF
Very reliable and you can even setup PlexPlus ST app to do different things for different content. For example, my setup will only turn the lights OFF if a “movie” is played and not for things like TV shows or YouTube videos. Plex Alexa skill includes full playback control as well.