How would you implement sensing the presence of a cell telephone ?

Discussion in 'The Projects Forum' started by Externet, Mar 30, 2015.

  1. Externet

    Thread Starter AAC Fanatic!

    Nov 29, 2005
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    Hi.
    For people passing trough a door, how to tell which carry a mobile telephone ?
    It would have to be of low sensitivity to ignore others outside or already inside.
     
  2. #12

    Expert

    Nov 30, 2010
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    6,840
    My computer speakers detect cell phones. :D
    I am often reaching for my cell phone because the speakers start clicking and I am wrongly thinking the phone is going to ring. :(

    Still, there must be a better way...but how to provoke a cell phone to betray itself?
    Maybe the way they detect televisions in the UK. Watch for its local oscillator frequency.
     
  3. wayneh

    Expert

    Sep 9, 2010
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    It's not selective for cellphones alone, but a metal detector would see one.
     
  4. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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  5. alfacliff

    Well-Known Member

    Dec 13, 2013
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    the problem is that cellphones do not transmitt continously when nobody is using it. they reply to pings from nearby towers, giving their id, so the system knows whitch towers can reach them.
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Do you need to detect cellphones which are switched off? Some people, believe it or not, don't suffer withdrawal symptoms when their phone is off :).
     
    #12 likes this.
  7. Papabravo

    Expert

    Feb 24, 2006
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  8. Papabravo

    Expert

    Feb 24, 2006
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    Or since money talks, just go buy one.
     
  9. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    it won't catch them all, but a good number will have their bluetooth on, which you can detect
     
  10. wayneh

    Expert

    Sep 9, 2010
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    Even more will have wifi on. Good point.
     
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