I don't think it's the distance really, it's the relaying and the additional steps that adds latency. If the data rate is low, and the data is not trivially sma

I don't think it's the distance really, it's the relaying and the additional steps that adds latency. If the data rate is low, and the data is not trivially small (ie over some 10s or 100s of bytes), you are in the milliseconds area, which should be very easily tracked. Perhaps if the keyfob needs to do some additional conditioning on the data (eg some decryption+encryption), or is very slow, the extra overhead of the relay is small in comparison. I don't know how the keyfob conserves power, but I guess some kind of duty cycling the radio, in which the first wake-up latency of the keyfob is not necessarily know beforehand. But, just send a few packets back and forth and get the overall latency and it should be able to determine if a relay is used.