WritingHacker: Audio Based Eavesdropping of Handwriting

I've been waiting awhile for the full scope of passive/near-ultrasonic/ultrasonic based attacks patterns to be mapped, and presented. I remember someone mentioned all that's needed is to compress & elaborate(reverbrative updating, frequency hoping[badminton attacks]), and you could full-sweep hack at a relative rate of 1-2 million physical devices at rate(I could believe full world sweep for the best hacker with about 2-5% reception loss[which has been the known rate mentioned in lore])