I ordered one of these bad boys as my OBD-II interface. It is an ELM327-based OBD-II scanner with bluetooth compatibility. This device connects to the car’s physical OBD port and reports car data over bluetooth. You also configure the device over bluetooth using custom AT commands.
I plugged it into my car, was able to connect to it with my laptop and send it AT commands over bluetooth. I was also able to monitor vehicle speed (in km/h) and engine RPM with the following commands and their responses:
To set up protocol → AT SP 0
Response → OK
To query vehicle speed → 010D
Response → 41 0D
To query engine RPM → 010C
Response → 41 0C
This website explains in better detail what the above commands do and how to interpret the responses.
I was also able to connect to the OBD scanner with my HC-05 bluetooth module. I wasn’t able to successfully send commands with my HC-05, but that battle will be waged another day…