How difficult would it be to use the 13.56mhz xnt tag to unlock your car door? What sort of hardware would be required.
Something like an Arduino and a PN532 for reading the tag.
You’ll need to find a way to control the car. Maybe by connecting the Arduino to the unlock and lock buttons on the inside of the car?
I don’t think the exact tag you’re using should matter.
I’ve built a circuit that powers a relay when authenticated with my flexDF, the only issue is actually connecting it to the vehicle. I’m still working that out on my van.
Connection to the vehicle is a real issue here. Honestly the easiest way is get a third car key programmed (if you still want a second spare), break it open, and solder a small relay to the different button pads. Best way (but doesn’t always work) is using CAN/OBDII but that takes a lot of work and doesn’t always work so YMMV.
I honestly don’t think it would be difficult to wire it into the car. Just take your driver’s door panel off, find the wires that operate the inside “lock/unlock” button, splice into them without cutting them, and wire relays to them so the relays are wired in parallel to the buttons. This way whenever your microcontroller activates the relays, electronically it is the same as hitting the button and the buttons still work.
I think the hardest part will be if you want it to look clean without having a visible reader on the outside. The range on these tags is super short and even planting a reader right behind a fiberglass door panel would probably be too thick for it to work. My xNT scans fine but even when I just had a bandage on it would not read.
Range is an issue, yes. The xEM has way better range though I’ve noticed.
I do know some cars (mine included) where the interior controls don’t work when the car has been off for a while. All depends per car and per manufacturer.