Simplifying the driver identification use case

Has anyone here successfully taken care of a use case where a client wants to know who was driving the vehicle at what time?

I'm looking for a simple solution where the RFID reader (or bluetooth dongle) automatically detects when a driver entered a vehicle, so it immediately updates the current driver of the vehicle without the driver having to manually put a card/tag near an rfid reader.

Goal is to make it as simple as possible so we won't have to deal with "driver forgot to read card" or whatever. We don't want to install immobilizers either as this would drastically increase the cost of the use case and the implementation period.

Please let me know if anyone has any ideas. I'd love to hear your stories!