A mysterious little box above my apartment door

Discussion in 'General Electronics Chat' started by mecablaze, May 20, 2014.

  1. mecablaze

    Thread Starter New Member

    May 20, 2014
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    I just moved into a new apartment and I noticed a little plastic box above my main entry door. I opened it up (single screw on the back) and found a little pcb with a A23 battery (12v) slot. I am by no means experience in the world of circuit boards but I typed up some of the numbers on the components and identified a microcontroller (12C508A) and some kind of wireless remote controller (303.825). There seems to be a push button switch and another switch which is triggered when the door opens (or closes...). When I open the door, a little red LED blinks once.

    So my totally uneducated guess is that it detects when the door is opened and broadcasts some signal.

    The strange thing is that the battery in there was dead. My question is this: what exactly does this board do and should I be worried that someone (landlord, previous owner) is spying on me? I can just take out the battery to disable it but my curiosity is piqued. If it is indeed sensing when the door is opened can I use it for myself? How would I know what kind of signal is being broadcasted (if any).

    I've uploaded pictures as an imgur gallery.
     
  2. inwo

    Well-Known Member

    Nov 7, 2013
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    Motels use door sensing for their smart energy management. I've worked on them a few times.
     
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  3. crutschow

    Expert

    Mar 14, 2008
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    Did you ask the apartment landlord about it?
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Maybe a previous tenant was prepared to be warned if he had an unexpected a visit from a member of the 'Heavy' mob?. :p
    (if so, hopefully they know he has moved)!
    Max.
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,094
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    That can is a transmitter (well part of one), and you can see the trace on the PCB that acts as an antenna.

    Makes you wonder where the receiver is. ;) Anyone could have "installed" it. You might be able to find your own receiver.
     
  6. #12

    Expert

    Nov 30, 2010
    16,261
    6,768
    It looks like part of a burglar alarm to me. Some of my customers have those.
    I just did a wireless doorbell last week and it looks the same except it has a big ol' button you press to make the doorbell ring.
     
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  7. mecablaze

    Thread Starter New Member

    May 20, 2014
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    Thanks for your help, guys. I've used my SDR dongle to detect the signal. Seven distinct pulses... I think I'll just leave it and use it for some fun home automation stuff. Hard part is the receiver. Wish I took those DSP classes in college.
     
  8. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    It also could have been used to detect when someone opened the door from the inside, i.e., alzheimer's patient or similar, and sounded an alarm. Either way, it was probably installed by a previous tenant, who moved away without it.

    Or maybe it was Mossad...is there a minora on it anywhere? :D
     
  9. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Are you in Europe or North America? If N.A., would you post a link to your SDR dongle? Thanks.
     
  10. panic mode

    Senior Member

    Oct 10, 2011
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    looks like old garage door opener, maybe used to open main door for visitor/pizza guy :)
     
  11. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    It's a similar box to a door opener, but is a dedicated RF alarm component. Note the tiny test button and the hole in the PCB designed for the wire to the external reed switch.

    There was probably one on the window too?

    Generally they come in a box set with alarm base station and a few RF sensor units, RF PIR sensors and RF reed switch sensors (like that one).
    :)
     
  12. alfacliff

    Well-Known Member

    Dec 13, 2013
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    do any of the other appartments have the box?if they do, its an appartment management thing, if not, its a previous owner thing.
    garage door opener transmitters usually operate somewhere around 308 mhz, modulated oscilator, so not very stable.
     
  13. Mike33

    AAC Fanatic!

    Feb 4, 2005
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    Bingo....looks to me like a unit I've seen used in group homes. If one of the residents were to get the door open, a loud tone is sounded inside via RF transmitter. Looks like they took the receiver with them?

    You can hack that for any number of great uses! I have PIRs from a house we restored, same thing - they give off pulses. But they are easy to hack.
     
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