circuit to detect active mobile phone

please help me
can any give me direction to design a active mobile phone detector with a range of 3 to4 metre or more i have searched for the circuit diagram but i got devices with a range of 1tp 2 metre only,please help me

You may boost the receiving range of the present circuit to more than 10 meters when you use a matched Yagi antenna which is highly directive.
Cheers

thanks sir