[svens_]

Don't worry, they thought about that:

Guests' privacy is always protected. Our patent pending technology ensures that no content is recorded

It's patented, so it must be good.

Sarcasm aside, I really wonder what's in that patent... I mean it must (should) exist, otherwise it should be "pending".

[robryk]

Given that variable bit-rate VoIP can reveal words spoken from bitrate alone[1], I would be very cautious about their claims.

[1] https://www.schneier.com/blog/archives/2008/06/eavesdropping...

[svens_]

I doubt their "signal processing" involves anything more than a microphone and a peak detector.

A more practical side channel attack would probably be through radiated emissions over the mains power. However if you're willing to go that far, a laser microphone is much more effective and simpler.

[robryk]

Depending on how wide is the peak detection window, they might send enough data to detect how long consecutive words are. I have a vague impression that I've read once that this, together with a language model, can be used to guess what's being spoken ~10% of the time or so.