When you sleep, your body moves slightly with each breath and heartbeat. A mat with 512 sensors under the sheets records these movements like a sensitive membrane. If breathing stops, that's dangerous, a condition called apnea.
Previously, it wasn't clear which movements mattered most. The researchers broke the signal down into many components: overall statistics, zero crossings, energy, wavelets, ten groups in all. Then they tested them on 155 patients.
Now it's possible to build simple devices: instead of 191 features, 48 suffice. Such a mat could work at home and warn of dangerous breathing pauses.
The median synchronization accuracy between the polygraph and the mat was 21 milliseconds, which is less than the duration of one frame at 50 Hz. This accuracy was achieved by transmitting a pseudo-random code through the EEG channel, like Morse code between two independent clocks.