Design a simple RF circuit

Design a simple RF circuit that will detect the presence of a cell phone. 1.0 Specifications 1.1 Cellular Technology - any cell phone (voice, text, or data) currently in use in the USA. 1.2 Range - maximum distance from cell phone shall be 10 feet (line-of-sight). 1.3 Detection rate - The detector shall detect the cell phone within 5 seconds of powering on the cell phone when it is in-range or 5 seconds of coming into range when the cell phone is already powered on. 1.4 Output - There shall be an on-board, low power LED (red) that shall be off when there are no cell phones detected and on when a cell phone is detected.  The LED shall remain on for a minimum of 5 seconds when a cell phone has been detected. 1.5 Power - the detector shall be powered from 3 VDC and shall consume a minimum of power 2.0 Deliverables 2.1 Schematic diagram (in any form) 2.2 Bill of Materials (in any form) 2.3 Working prototype 2.4 Circuit description 3.0 Design Criteria (in order of importance) 3.1 Ability to reliably detect cell phone 3.2 Low power (the power consumed by any circuitry used to stretch the on-time of the LED shall not be considered for this criteria). 3.2 Small physical size (this does not need to be demonstrated on the prototype)