Quick and non-blocking method to connect the OBD-II? about arduinoobd

[MichaelPate]

In terms of hardware, if you are trying to quickly see if the vehicle is off, you could poll for voltages on the ignition switch (or perhaps the data lines) and then attach that to one of the Arduino's inputs, using proper protection where appropriate. Then adding a "kill switch" to the code would tell you instantly if the car is off. No voltage, the car must be off.