Hi @SHL, thank you for reaching back to the Sonos Community, and thanks for letting us know your concern here. Let me help you with this.

First, let me ask some questions to isolate the issue so we can create a path towards resolution.

1. Did you set up Alexa on your Sonos Arc? If not set up, Alexa won't be able to find it.
2. Is Alexa respond when asked about the weather on the Sonos Arc?

If you have set up Alexa on your Sonos devices with voice-enabled capability, let me suggest basic troubleshooting steps to see if this would work for you.

1. Open the Alexa app on your iOS or Android device.
2. Open the menu in the top left and tap on Skills & Games > Your Skills > Sonos > Disable Skill.
3. Deregister your Sonos speaker from Alexa by following the instructions on Amazon's website: Deregistering a device.
4. Disable Voice Control in the Sonos app. From the Settings tab, tap Services and select Amazon Alexa under Voice. Select the voice-enabled speaker from the list of Sonos Products, and tap Remove Alexa.
5. Log out of all Amazon Apps on the mobile device, including the Amazon app, Alexa app and Amazon.com in your mobile browser.
   • To sign out of the Amazon mobile app:
     • On Android devices, open the app and tap Menu > Your Account > Sign Out.
     • On iOS devices, open the app and tap the menu icon in the top-left corner, and then choose Settings > "Not gname]?"
6. Using the Sonos app, complete Alexa setup again. Follow the steps to log into the appropriate Amazon account when prompted to do so.
7. Once completed, try giving Alexa another command.

If you're experiencing the same,  please submit a diagnostic report to further check on this. Let us know the confirmation number.

Let us know how it goes. We'll wait for your reply.

Thank you @Rowena B.   I performed every step you prescribed and ended up at the same place. When I issue the voice command “Alexa turn on the TV” to my Sonos Arc, Alexa responds “Sorry I didn’t find a device named TV.” 
As I stated in my original post, this response from Alexa would be fully expected if I were issuing the command to any other Alexa device (Echo Dot or whatever), as I don’t have a TV connected to Alexa in any way. So, again, I’m confused. Why is Alexa responding to this voice command via the Arc when the Arc should just be sending a power-on command through my TV’s HDMI-ARC port, bypassing the Alexa network altogether?  If this were working properly, and the tv did actually turn on, would Alexa still be responding that it didn’t find a device named TV?

FYI, I have an open support case on this issue, and already submitted diagnostics. The analyst was stumped and saw nothing unusual in my diagnostics. But they should be attached to the case if you want to look at them. 

Hi @SHL, thank you for your quick response and for performing the troubleshooting provided. Let me check what I can do.

Looking at the error - "Sorry I didn’t find a device named TV." Did you name your Sonos Arc as TV?
Have you tried asking Alexa specifically like for example "Alexa turn on the TV in the Bedroom."?

My apologies but we don't have access to your account from our end to see your current ticket or the diagnostic report. This is why we asked for the confirmation number to check it.

I really appreciate the time and effort you've spent doing all the troubleshooting steps, and it would be best for you to continue working with us over the phone to expedite the process. 

I recommend contacting our Sonos Customer Care. Our phone support has the tools to check what's going on in your system and remotely access your device and to provide the best option for you.

Let me know if you have any questions about this. We and the community are always here to help.

Thanks again @Rowena B. and I will call in tomorrow. However, your questions prompt even more confusion on my part. 
First, my Arc is named Living Room in the Sonos App and in the Alexa app it is called the same when it is discovered, which is “Living Room” (with an icon that resembles a speaker).  I have read, and re-read, all the articles/instructions around setup of the Arc, and everywhere it simply instructs me to tell Alexa to turn on the tv and it should work. 
When I state the command “Alexa, turn on the __________,” what should I fill in the blank with?  The name of my Sonos Arc as Alexa recognizes it? Simply the word “TV?” “TV in...” room where my Arc resides? Or something else? 
I realize I may sound redundant at this point, but if the TV-ON command is going from Sonos to my TV through the HDMI/ARC port, how/why is Alexa involved in that? How would Alexa know anything about my TV, which is connected directly to the Arc but not part of my Alexa ecosystem? 

Hi @SHL, thank you for your reply. My apologies for the confusion.

Alexa control for your TV requires an HDMI-ARC connection between the TV and your Sonos home theater product. There shouldn't be any problem with your setup. We are trying to isolate the issue by asking Alexa specific commands if she's going to respond correctly.

• Have you tried asking Alexa to turn on the TV in the living room? - "Alexa, turn on the TV in the living room?" 
• When the TV is on and you ask Alexa to turn up or down the volume, did the volume change?
• How about asking Alexa about the time and the weather? Did she provide the correct time and location?

If in any of these commands Alexa responds incorrectly, it would be best to check this up with our phone support to connect to your device and see what's going. 

Please feel free to reach out in the future if you have any other questions.

@Rowena B. Ok. “Alexa, turn on the TV in the Living Room” finally worked. I guess that clears up the big mystery. However, the opposite command - Alexa, turn OFF the TV in the Living Room - has no effect. Based on other postings I’ve seen in the community, there are apparently some TVs that won’t accept on OFF command thru the HDMI-ARC port. I can only guess my Samsung Frame is one of those. 
I’m happy that the on command works now. I can live without the OFF command working (although it would obviously be nice if there were a fix for that, but I suspect that’s an issue with the TV). 
Thanks for the support. Might be worthwhile updating the Sonos articles on this topic - unless I completely missed it somewhere, there was nothing indicating you needed to specify the room location in the command. 

Hi @SHL, thank you for keeping us posted on this. We really appreciate it. 

I'm glad that one of the commands worked with Alexa and recognized the living room to turn on the TV. However, there are still some commands that Alexa unable to respond to.

To further assist you on this, you may reach our Sonos Customer Care support to remotely access your device and check what's going on.

If you need help with any other information, please be sure to let us know.

We're here to answer any further questions you have.
 

I think I am having the same issue.   Also a Samsung frame TV (with a Beam) in “main bedroom”
 

I have an Arc in another room (basement).  That works if I use the full command (Alexa, turn in the tv in basement). 
 

but doesn’t work in main bedroom.   
 

I did move around gear.   I assume this issue happens for early adopters with a lot of gear and possible name conflicts. 

Hi @jfranche, 

Thanks for reaching out to the Sonos community and for letting us know about your concern.  What was Alexa’s response when you give a command in your main bedroom? To help you check why Alexa is not working in the other room, I'll be requesting a diagnostic report submitted from your Sonos system. Please don't forget to include the confirmation number in your response to look into your system and find out the cause. We'll wait for your reply.

Feel free to reach out if you have further questions or concerns, we’ll be glad to assist you.

Thanks Rowena.  
So after ignoring it for a day.   Now Alexa (from Beam) will turn on the Samsung Frame TV.

Asking it to turn off.   Or “switch to TV” commands do not work.   But I have heard others with those problems.  
 

PS my tips below on troubleshooting these sort of things:

ensure no name conflicts between rooms/groups used by Sonos, Alex and Apple HomeKit  

TVs have settings   You maybe need to enable CEC, hdmi-arc, anynet+

reboot home router

Turn off and on gear being used  

disable/enable Sonos skill in alexa

add/remove voice service for device in Sonos app

wait a day for things to settle in