Comment Re:old news... (Score 4, Informative) 96
What you describe is called indirect TPMS. It works by measuring the differences in speed between wheels through the ABS wheel speed sensors, and triggers if it detects an outlier. It doesn't require an additional sensor inside each wheel, instead using existing sensors and some arithmetic, so it costs less, but cannot indicate the pressure for each individual wheel, plus it requires the reset procedure that you referenced when new tires are installed or after you've corrected whatever caused it to trigger. My 2004 BMW has that, and so did Mazdas into the current decade.