sounds rather complicated. You would have to scan the entire spectrum (not the entire, but like certain bands) and detect if there is someone sending power on t

sounds rather complicated. You would have to scan the entire spectrum (not the entire, but like certain bands) and detect if there is someone sending power on there. But modern vehicles detect these relay attacks and drop your message when you are too far away (ToF Measurement), you could maybe instrument that. But then when you walk to your car on an open field, you may also trigger the alarm because your key is out of range for a short time.