Wireless tracker (Very Very Small Transmitter and Receiver)

I need very small transmitter cum receiver... the task given to them is to give a response signal if asked simply like tracker device...
I reviewed many Tx-Rx modules but they are used for communication purpose so they are bulk... i need them to hold within a pendrive size as they should use very small power and only one purpose should respond to a particular frequency when tracking signal is send the range can be 2-3Meters...

What is your particular frequency ?
I think an LNA+Detector circuit will give you a signal strength as DC voltage...
But those are depended on signal level,frequency and modulation if there is..
A very small LNA can be done a single Low Noise Transistor with very small package and this amplifier may be optimized for single frequency,no doubt.
Antenna can be placed on PCB and detector circuit can also be implemented on a single PCB.

Any range of MHz-GHz but my aim is size and power consumption with only one thing that it should give response signal (like i am present) using the strength of the signal given by this module the distance can be calculated.... i hope i am right till now...