The trick with a well-implemented smart home system is to consider failure modes in the design phase. I made my own "smart-kettle"[1] which does work with Alexa but when the Internet is down it reverts to a regular kettle with regular buttons.
Similarly, smart lights are often problematic for a range of reasons. Most need to use an app to control them, or some incantation for Alexa to do the same, neither of which are discoverable (or maybe even accessible) to someone in your house who isn't you. If you have them connected to a regular light switch, they stop being "smart" when someone uses the light switch on the wall to turn them off. All of these problems are easily addressed by using smart switches instead of smart lights. Everybody knows how to use a light switch, and any failure of your "smart" systems means the light switch still works like every other light switch out there (meaning, get off your butt, walk over to the switch and it turns lights on and off).
This concept holds true in my house for garage door openers, door locks, fireplace controls, and a whole raft of other stuff. The existing systems function like they should to a user who knows how a garage door opener (or whatever) is traditionally supposed to work. In addition, they get some extra functionality[2] if everything is up and working as designed. If things aren't working... well you have to press the garage door opener button like it's 2010.
[1] https://hackaday.io/project/20217-iotea-kettle
[2] https://github.com/aderusha/MQTTCarPresence
Similarly, smart lights are often problematic for a range of reasons. Most need to use an app to control them, or some incantation for Alexa to do the same, neither of which are discoverable (or maybe even accessible) to someone in your house who isn't you. If you have them connected to a regular light switch, they stop being "smart" when someone uses the light switch on the wall to turn them off. All of these problems are easily addressed by using smart switches instead of smart lights. Everybody knows how to use a light switch, and any failure of your "smart" systems means the light switch still works like every other light switch out there (meaning, get off your butt, walk over to the switch and it turns lights on and off).
This concept holds true in my house for garage door openers, door locks, fireplace controls, and a whole raft of other stuff. The existing systems function like they should to a user who knows how a garage door opener (or whatever) is traditionally supposed to work. In addition, they get some extra functionality[2] if everything is up and working as designed. If things aren't working... well you have to press the garage door opener button like it's 2010.
[1] https://hackaday.io/project/20217-iotea-kettle [2] https://github.com/aderusha/MQTTCarPresence