Just have found another interesting piece for this thread. Reading next devices manuals, looking for one with BT off switching, there is a sentence: 

“About Bluetooth communications
Radio waves broadcast from this unit may interfere with the operation of medical devices. Make sure you turn off the power of this unit and Bluetooth device in the following locations as radio wave interference may cause malfunctions.
- Hospitals, trains, aircraft, petrol kiosks, and places where flammable gases are generated
- Near automatic doors and fire alarm”

So many potential clients are excluded this way. The possibility of switching off BT would stop their protests with banners “Network speakers for everyone!”, “Ethernet rulez!”  ;-)

Did that device use Bluetooth or Bluetooth Low Energy?

I have several Bluetooth LE devices that do not have that warning.

Who knows :-) 

I've noticed that manufacturers don't like to brag about the transmitters they put in their devices. Here is the source of the instructions for the equipment I wrote about (not cheap one):
https://assets.denon.com/documentmaster/master/ceol_n12_owners-manual-eu-en.pdf
Interestingly, the fine print in this manual states that you must turn on Bluetooth on your phone if you use the phone app to control the device (HEOS app). It's unclear whether it's only during installation or all the time, but from the description it looks like it's all the time...
There are probably some meters to measure whether the device is transmitting something and I would gladly buy it, but they are probably expensive toys.

That doesn’t sound like they’re using Bluetooth Low Energy: “you must turn on Bluetooth”. If so, comparing energy emissions like this and Sonos BLE is rather like comparing apples and oranges. And not knowing for sure makes it more like comparing apples with chalk. 

I did find this tool. I cannot vouch for its accuracy or effectiveness.

I don’t know.  I’ve taken a bite out of some pretty bad apples before.

Let me share the knowledge I collected after some research:

- as Sonos support answered to me, One SL, One (Gen 2), Five, Sub (Gen 3) products utilize Bluetooth low energy (BLE) during setup. After the speaker are set up, the BLE is stopped, you can connect the Sonos devices via Ethernet cables and then disable the WIFI from the Sonos app for the Sonos products and they will work only on the Ethernet connection. I was looking at One SL - it really has a special button to press only during the initial setup
- new Sonos models (as production of One SL has just stopped) for example Era 100/Era 300 have no BLE, we can use an external USB C Ethernet adapter (additional cost) to work wired. After the setup, we can disable the WIFI from the devices and they will only work on the Ethernet connection. The Bluetooth is disabled by default, to start the Bluetooth setup on the Era 100/300 we will need to press and hold the Bluetooth button on the back of your Era until we hear a chime. The front status LED will start flashing blue, and then the speaker will start to search for nearby Bluetooth speakers.
- there is another company - Bluesound, for example, their speakers (Pulse Flex 2i), are nice, with the possibility to add a battery “back bag” - making it movable. We can switch Bluetooth/WiFi off in options.
- Denon speakers - no way to get human support, they send me links to FAQ or AI-prepared answers. No Bluetooth off option in the app, they use a “sleeping” system, but how it works is described very lapidary (probably we always have to wait 20 min for “sleep” Bluetooth/WiFi)
So, the Bluesound options seem to be ideal, but the speakers are expensive. Sonos Era 100 plus Ethernet dongle - also expensive. Sonos One SL - model, from 2018, not produced starting this year and how to check if BLE is off indeed? (any way - very attractive economically) 

I have also found a Erickhill ER02 electro-emission meter - I would like to make sure, that all the above is true in real life, but I do not know if this meter will be suitable to measure that. Maybe someone knows?

Which one “cheaper/older” you mean? Are you sure they do not use BLE? Please notice, that you can never be sure - a word “bluetooth” is nowhere in manual, nowhere in specifications of One SL. And? And suddenly you find out that there is BLE. Not fair on Sonos. More of it - I also had a chat with their support (see my post above) and they said that “One SL, (...) utilize Bluetooth low energy (BLE) during setup. After the speaker are set up, the BLE is stopped” and? And as you can read here several people measured that it is not stopped. Not fair again. 

When you use the speaker on your desk, working remotely, emission for hours every day, close to your head - is not without significance.

When you plan to install an multiroom audio system in a little medical clinic where there are medical equipment with prohibition of using BT nearby - is not without significance.

So Sonos, please make your manuals more transparent, please let people switch on only that audio transmission, they really need.

​

If you are concerned about “emission for hours every day, close to your head”, I strongly suggest you refrain from buying any WiFi speakers; regardless if they allow you to turn Bluetooth off or not.  Also stay away from cell phones, microwaves, plane rides, sunshine, walks outdoors, and other activities which expose you to EMF levels which exceed that of BLE by tens of thousands to millions of times. 

Thank you vey much for your clever advice! 

Greetings! 

I'm serious.  Being worried about BLE and not those far more powerful sources of the same type of EMF radiation is like being worried about red dye in one M&M while smoking 2 packs a day, drinking irradiated barium shakes for every meal, getting chest X-Rays for fun, and taking your biannual month long trips to sunny Chernobyl.

That’s a bit of an exaggeration. It’s more like 1 pack a day, and the barium shakes every evening meal.

I have Bluetooth LE hearing aids, stuck behind each ear for about 18 hours per day. Looking at RF total exposure levels they are still likely lower than the 2.4 & 5 GHz access point I’m five feet from, my tablet that is in my hands several hours a day or the cell phone I’m usually three feet from unless it is in a pocket.

If you are serious you need to prioritize the RF issues and solve the worst ones first.

I too would also love to turn the BT and WiFi off. No, I am not some bozo that’s scared of 5G. If that was a problem I am sure growing up below a radio tower would have killed me by now. I do however have an inordinate number of electronics at my home and the wifi spectrum is at a premium. I just realized what Sonos was doing and it SUCKS for wifi. If I can’t figure out how to disable it, I will try to physically remove it, and if that doesn’t work its going into the trash. (Sound is meh anyway.) For the price, I am rather disappointed… especially that the programmers are really that lazy. Multicast? seriously? 

Anybody who is so obviously unaffected that they can carelessly throw $200+ of electronics in the trash, and yet are angry enough to bother to register here and say so in their very first post, should be ignored.  

Look at the list of products @rexabush has; it’s a heck of an investment for products where the “sound is meh”. 

Yeah, $3,000+ listing, both S1 and S2, first ever post.  It's much easier to spot when they try too hard.