communicating electronics modules

Hi all. Can any body help me with this project. The project concept is like this: there are two small modules with their own battery and small PCBs with electronics. both the modules have small coils which generate magnetic filed around them. when these modules are in proximity (i.e. say 10cm), the start beeping/flashing light. any ideas about the project please share. thanx in advance..

There are a few problems associated with this scheme. 1. Must BOTH modules flash?, it would be much simpler to have transmitter module that just detected the receiver module (or the other way around?). 2. The 10 cms, is this meant to be symetrical, i.e. the modules can approach each other from any direction for the alarm to go off at 10 cms. The reason is that it is very difficult to generate a uniform circular RF field. The only way to do it is to have the coil with its axis vertical, or a vertical dipole, either way the RF will be directed at the electronics and the floor and ceiling.
Frank

for the starting, thats the idea. only one will transmit and one will receive and beep.
But i'm thinking of a coil rather than an antenna. And the distance will be 10cm in one plane only. see the attached pic.