Detect / prevent the use of range extenders?

[JB21]

Is there any way to detect / prevent the use of range extenders?

When using a central & server with low TX power, the range is say 10m. Now an attacker can use a relay where central & client unknowingly connect to and thus increasing the range. For encryption we can only use Just Works, and the relay can also use that. So that's no help.

Is there any way to detect the longer travelling time of messages? If the relay uses short connection intervals then the added delay may just be too small to be detected?

Any ideas?

[JB21]

It's an access control system. That should only work within say 10 meters. Similar to touchless keys used by cars. And there criminals have used 2 extender units, one near the car the other near the owner with his key who sleeps in a hotel. Quite easy to open a car.

No, I'm not that worried about unauthenticated devices trying to connect. It has been taken care of.

Assume the central uses the shortest connection interval and does a characteristic read, then it should get a reply just an interval later (2.5 ms), right. Can one rely on that?