If the device is ‘off’, how would it know/ receive a signal to ‘wake up’? 

I love the result, I’m not sure I understand how it works, unless Sonos adds a third state, in between off and on. 

I used to own the Bose Soundlink Micro and on connecting via Bluetooth it wakes up from a powered off state. I would often use it to locate the speaker if i can’t find it around me. 

The Bose SoundLink Micro utilizes Bluetooth Low Energy (BLE) for its "always-on" functionality, enabling it to be discovered and connected to by your phone even when the speaker is seemingly off. BLE allows for low power consumption, meaning the speaker can maintain a low-power connection without significantly draining the battery. This enables features like the ability to turn the speaker on remotely via the Bose Connect app or by initiating a connection from your phone. 
 

BLE is used to keep the SoundLink Micro discoverable by your phone, even when the power button isn't actively engaged. This allows for a seamless connection experience.

Right, so the Bose isn’t off, the way that the Sonos is, it’s just asleep. Kind of like leaving your Sonos ‘on’ and it moving to a low power state, which it already does. At that point, it is waiting for a ‘wake up’ signal, via Bluetooth or WiFi. You just need to not fully power down your Sonos. 

You’re not getting it. My bose would be completely powered off but technically it is not completely powered off i don’t know. I just want something similar replicated on Sonos’s portable speakers. 

Sounds like it would take a hardware redesign to provide power to the new connection while the rest of the speaker was powered down.

Don't know how that would impact battery life with the constant, but low, power draw.

If I’m not mistaken, the Sonos already offers this, just don’t turn it off. It enters that low power state automatically, after not receiving any audio signal, and waits for the ‘wakeup’ signal you’re suggesting. 

I think you should go get a bose soundlink micro and see for yourself.