Proximity detector with data logging?

I am thinking about a project that would link one arduino(as a master) with several arduino nanos. The idea is to data log when the nanos(registered to a specific person) come within 30 feet(roughly ten meters for my European friends) of the main . I'm trying to make it as reliable to that distance as possible, and of course, make as few false starts as I can!

The biggest trick is that the range can't extend too far beyond that(a false alarm), or too far in(too little warning).

My first thought is a call/response system wherein each transceiver would have a limited range, and the combined range would average out to about my 10 meter goal.

The data logging isn't entirely necessary, but would be a valuable feature.

My first concern is: What to use as a detection system? I'm looking at either a Bluetooth system or something using a tx/rx radio frequency system.

Any information, advice, or warnings anyone could offer would be greatly appreciated.