Today, most cars allow wireless unlocking, but some newer models have started to use a NFC login system (like NXP car’s showing on the MWC) so you can use your smartphone as a key.
With this tutorial, you will be able to easily build your own NFC door control with a Keyduino or an NFC shield and a relay shield in only a few hours. Note that you can use a BLE shield instead, but use an NFC ring to unlock your car is really cool.
You can find the code for the smartphone, the APK and the KeyDuino files (you can use it with an NFC shield connected on HSU) on this github.
The code with a badge/NFC ring is included the KeyDuino lib (example>relay shield).
Also when I use my normal key to lock my car (407 Peugeot), I cannot use the central unlocking anymore. So you will need to lock the doors by the NFC system. It’s a basic project so there is no power consumption management and the security is based on a NDEF password.
Still in progress
I am currently working on an improved prototype with a BLE+NFC board directly on the car handle (flexible pcb for the NFC antenna).