are there companies that produce systems that can detect the presence
of a cell phone in close physical proximity or detect the location of
a cell phone?

Hello, jheller-ga!

 There are, indeed, companies that produce devices that can not only
detect the presence of a cell phone, but can also decipher their
location. I have highlighted some below:

The Zap Checker
***************
http://www.zapchecker.com/what.html

The Zap Checker:
  "The Zap Checker is an Ultra-Sensitive instrument that detects and
displays electromagnetic radiation over a broad spectrum of
frequencies."

Uses:
 The Zap Checker measures electromagnetic radiation from 10 MHz to 4.5
GHz. This includes a variety of household devices:

Cellular phones and wireless (portable) phones 
Microwave ovens 
Transmitting security and baby-monitoring devices 
Electronic car keys and garage door openers 
FM radio and TV broadcasts 

Also detects and measures radiating signals from: 

Hidden transmitting cameras, transmitting phone bugs, surveillance
equipment and covert microphones
HAM radios, FRS walkie talkies, citizens' band, VHF and UHF
communicators
Police and emergency services transceivers 
Transmission line leakage from wires or cables 

Read more about the Zap Checker's Applications for use at 
http://www.zapchecker.com/apps.html


Cell Block Technologies, Inc
******************************
http://www.cell-block-r.com/

"Cell Block Technologies’ principal product line consists of
Cell-Block-R Systems.  A Cell-Block-R System can detect and control
the use of cell phones within limited restricted areas.

The cell phone silencer system blocks incoming calls and may record
the identity and location of any cell phone left on.  If an attempt is
made to make an outgoing call, the system can prevent the outgoing
call, send an alarm and report the exact location of attempted
infractions.  The system is not a cell phone jammer.  There are three
models: Detect-only, Prevent-only, and Prevent-Record-Alarm.

Detection:
http://www.cell-block-r.com/Technology.htm

Products that detect the presence of cell phones and send an alarm
when one is present cover another approach to the cell phone abuse
issue.

Morse Medical Inc. and Zetron’s Cell Phone Detector Plus are available
products using this approach.

Detecting cell phones is legal in all jurisdictions of which the
Company is aware.  Unfortunately, detection provides absolutely no
assurance that a user will turn off their phone or refuse to use it.

Morse Medical - Model 510
Morse Medical Inc. Model 510 senses intentional and inadvertent
operation of cellular telephones and hand-held radios in such
restricted areas. Once a   cell-phone or hand-held radio signal is
detected, the Model 510 provides notification in the form of an audio
alarm followed by a   voice message. The voice message requests the
cell-phone user to discontinue use of their cellular telephone. A
switch behind the front panel allows the user to set the Model 510 to
use voice plus alarm or alarm only.

Zetron  Cell Phone Detector Plus
Cell Phone Detector Plus detects mobile phone and 2-way radio
transmissions. It sounds an alarm followed by a voice message
requesting the user to turn their communication device off
immediately.  Compact and lightweight, the Cell Phone Detector Plus is
portable or can be easily wall-mounted. For convenience, the Cell
Phone Detector Plus can be powered by batteries or an AC adapter. It
has an adjustable detection range of 2 to 30 meters outward from the
unit.

Read more at http://www.cell-block-r.com/Technology.htm

 **** Just for your information, there are some very annoying little
letters and numbers that follow your mouse all over the above
page!!!!!! Sort of neat, but irritating!!!


Cell-Phone Detector Plus  
************************
http://starportuk.com/61.htm

Upon detecting cell phone or 2-way radio transmissions, the Cell-Phone
Detector Plus sounds an alarm followed by a voice message requesting
the user to turn their communication device off immediately. Advanced
features include detection of both analog and digital cell phones,
alarming upon Standby mode signals (when a cell phone is ON but a call
is not in progress), and a remote alarm output for connection to an
external device such as an annunciator panel or alarm system.

Hidden, front-accessible controls and external input/output jacks make
it easy to adjust the CellPhone Detector Plus for a specific coverage
area, detection method, or alarm mode.

Advanced features include detection of both analog and digital cell
phones......

(You can read more specifics on the above website.)


Additional Information
**********************

From "Wireless Channel Security Tutorial," by Steve Russell. Iowa
State University
http://216.239.53.100/search?q=cache:YxLXz-281qoC:www.public.iastate.edu/~sfr/wireless/w_tut_1.html+detecting+presence+of+cell+phone&hl=en&ie=UTF-8

"Location ECM is used to locate and track wireless transmitters in the
network. Programs now exist where a cell phone user can be located
down to the cell site and antenna sector level."


You might be interested in reading a forum thread titled
 "Re: IP: Detecting Cell Phones Used As Bugging Devices" at 
http://www.interesting-people.org/archives/interesting-people/200206/msg00032.html


Another interesting article titled "Halting cell-phone mischief" which
highlights a company called "Netline" can be found at
http://archives.openflows.org/electronetwork-l/msg00388.html:
 "What enables Netline to detect them (cell phones,) however, is that
they periodically transmit a signal to their base station. Netline's
small Cellular Activity Analyzer is a device that can be left in a
boardroom, for instance, where it can detect and record cell-phone
activity and give visual and audio warnings.

  
 If you need additional clarification, or any of the links don't work,
please don't hesitate to ask!

 Thanks for your question!

umiat-ga  
 
Google Search
+detecting +cell +phone +proximity
detecting presence of cell phone
detecting cell phone

thank you