The AirSense 11 has a microphone that listens to your mask

[srlevine1]

I'm going to order McDonald's food through the mic.

And realize the Mcbill is more than a top quality mask.  

[SarcasticDave94]

If I tried talking with a mask on it'll sound like at an old McDonald's drive thru, or Charlie Brown's teacher.

[tanker]

I turned off AccousticSignal several days ago. I checked today and it's back on! How can I make sure it stays off?

[Thunderclap]

An acoustic sensor is no more a microphone than a light sensor is a camera. Identifying an apnea event through the mask tube doesn't require fine acoustic circuitry, fidelity, timber or density... it's LOUD! In all things engineering you follow KISS or fail: Keep It Simple, Silly. There is no need to get all paranoid over a simple acoustic curve form profile analysis. There is no microphone assembly because it would be totally unnecessary and... useless. Haven't you ever actually heard an apnea event?

Don't allow your paranoia to deny you the health assistance of an acoustic sensor alert monitor. Apnea killed my father and is slowly strangling me to death. I take this serious.

[srlevine1]

An acoustic sensor is no more a microphone than a light sensor is a camera. 

In today's sensor-rich environment, you would be surprised at the information leaking into the ether and how it can be sorted, sliced, diced, and combined with disparate third-party databases. 

Example: the biometric data captured by a smart TV that can determine the biophysical reactions of users.  This smart TV displays health information based on viewers’ facial features

By recording keystrokes and training a deep learning model, three researchers claim to have achieved upwards of 90 percent accuracy in interpreting remote keystrokes, based on the sound profiles of individual keys.

In their paper A Practical Deep Learning-Based Acoustic Side Channel Attack on Keyboards (full PDF), UK researchers Joshua Harrison, Ehsan Toreini, and Marhyam Mehrnezhad claim that the trio of ubiquitous machine learning, microphones, and video calls "present a greater threat to keyboards than ever." Laptops, in particular, are more susceptible to having their keyboard recorded in quieter public areas, like coffee shops, libraries, or offices, the paper notes. And most laptops have uniform, non-modular keyboards, with similar acoustic profiles across models.

Read more at AI researchers claim 93% accuracy in detecting keystrokes over Zoom audio - Ars Technica

ResMed has the largest sleep apnea datastore in the world, keyed to individual machines and users by device numbers. Where did you think those modems and card-to-cloud data went?  I do not find any published benefit linked to an acoustic sensor at this time. 

Acoustic Sensor Technology

Built into every Air11™ device, acoustic sensor technology helps monitor hardware reliability and aims to provide future innovation in ResMed CPAP therapy solutions. Designed with strict privacy protections, the acoustic sensor enables ResMed to deploy features such as Device Diagnostic and AcousticSignal. ResMed Product Support - AcousticSignal 

Who knows what the future may bring. Fingerprinting your device is possibly a safeguard against Chinese fakes. But, you are correct: Don't let paranoia interfere with your therapy.