Spectre I [from Deveillance] is a portable audio security device that creates a 2m protection zone around you. It sends out signals that are inaudible to you but can be detected by a microphone. Through customization of the signals to match the human voice, your conversations are "overlayed" when a microphone receives them.
Pre-order available now.
Looks amazing! I remember seeing a YouTube video with a musical/tech influencer using something like this. I guess they just made a product out of the idea. Don't know if I can justify paying $1100 for it though. The cheaper way is to leave your phone at home!
Leaving your phone at home only reduces by one the indeterminate count of listening devices.
A countermeasure like this takes out all opportunistic recording, however an adversary could plan specifically for recording you: if the adversary places multiple microphones [two could suffice, three would be ideal] at known locations, then they can process the joint recordings and separate the concealment noise from the desired signal.