listening. sit still about a meter away, give it six seconds.
--br/min
HOLDING
chest moves -- mmheart -- /min
nearest surface echo ranging
--m
movement two-pulse canceller
still
what the mic hears 15 to 24 kHz
the glow is the chirp. you cannot hear it. the phone can.
BAT
the phone screams at 18 to 21 kHz, far above what you can hear, and listens for the echoes. that is enough to range walls, catch a hand moving, watch someone breathe from across a table, and on a good day count their heartbeat.
1 media volume all the way up
2 allow the microphone
3 set the phone down, face up, on a table, or stand it half-open like a laptop with the hinge toward you
how it works
the speaker plays a 43 millisecond sweep from 18 to 21 kHz, over and over. sound covers 343 meters a second, so every centimeter of distance delays an echo by a known amount. the page correlates what the mic hears against the sweep it sent and gets a map of every reflector in the room, good to a few centimeters. the phase of each echo moves when the thing that made it moves, and at these wavelengths a chest rising a few millimeters swings that phase through half a turn. hand-written signal processing, no libraries, nothing leaves the phone, no audio is kept.