@KubaW You will need to retrofit the complete keyless system. Wiring, antennas, KVM, IAU, SCU, door handles, keyfobs etc. Just keyless start without the rest is not possible. If you want to use a used KVM, you need to read the KVM IMMO pin from it on the bench to pair it with your car via Vdash. Your car will not be serviceable at any Volvo dealer anymore. At least not without some effort in reverting the complete retrofit.
If you use a virgin/brand new KVM, it needs programming with an official VIDA subscription which means the whole retrofit will be registered at the Volvo VIDA servers and the car stays "original", but this will be really expensive.
For part numbers you can find a thread in this forum where VIDA2014D/2015A is offered, or send me a PM. The EWD (wiring diagrams) for your car can be found online directly from Volvo here
