I'm pretty sure they're just an OBD II module. All cars after a certain date ('96, I think) have that connector under the dash somewhere.
I bought a couple modules from Gearbest a couple of years ago and used an android app called Torque to monitor more detailed car data on 3 different vehicles.
I imagine the app takes it up a level and correlates the data to some elementary maintenance procedures.
Some insurance companies use them to monitor your driving habits (mph mostly) to set insurance rates.
Oh, and it also reads engine codes.
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Last edited by basicbill; 08-07-2017 at 10:54 PM.
Reason: add more info.