The parking sensors on the MS and other manufacturers' cars appear very similar, suggesting to me that they're made by only a handful of vendors. As I understand it, they are small sonar units that emit a pulse of ultrasound and listen for an echo, a modern version of the big sonar rangefinder on the old Polaroid SX-70 camera (I'm dating myself). Sitting in traffic behind another car with an array of similar parking sensors tonight, I got to wondering how they all don't interfere with each other (both between different cars and even among the different sensors on one car causing cross-interference). I couldn't find a decent explanation online. Frequency hopping? I thought I'd post this (admittedly geeky) question to my fellow geeks on TMC to see if someone knows the answer who can explain.