Which type of sensor should i use to get RPM of an engine? Using Arduino (i got leonardo and uno),
I'm looking for a way to get the RPM of my car's engine.
I know this can be done using an OBD2 connection however i'm looking for a different way.
Sensing?
I need a reference for a sensor / a creative way to get this data.
Having said that, these approaches came up:

guessing the RPM by reading the amps in the car's 12V connection
recording the sound of the engine using a microphone and setting thresholds for certain RPM values
I would think something like this would benefit you greatly. If your vehicle was produced after 1996 it will have an OBD port near the steering wheel that allows you to read diagnostic information from the car. This diagnostic information always includes error codes (think: Check engine light), and often includes operating information like speed and engine rpm.