Open your Hackerspace Door with a Phone Call


[Mário] sent us a tip detailing the access control system he and his friends built for the eLab Hackerspace in Faro, Portugal. The space is located in the University of Algarve’s Institute of Engineering, which meant the group couldn’t exactly bore some holes through campus property and needed a clever solution to provide 24/7 access to members.

[Mário] quickly ruled out more advanced Bluetooth or NFC options, because he didn’t want to leave out members who did not have a smartphone. Instead, after rummaging around in some junk boxes, the gang settled on hacking an old Siemens C55 phone to serve as a GSM modem and to receive calls from members. The incoming numbers are then compared against a list on the EEPROM of an attached PIC16F88 microcontroller, which directs a motor salvaged from a tobacco vending machine to open the push bar on the front door. They had to set up the motor to move an arm in a motion similar to that of a piston, thus providing the right leverage to both unlock and reset the bar’s position.

Check out [Mário's] blog for more details and information on how they upload a log of callers to Google spreadsheets, and stick around for a quick video demonstration below. If you’d prefer a more step by step guide to the build, head over to the accompanying Instructables page. Just be careful if you try to reproduce this hack with the Arduino GSM shield.


  1. Per Jensen says:

    Cool hack, not so cool using a complete PC setup to run the brains of it …

  2. greenbacks says:


  3. eldorel says:

    Using callerid for access control is a really bad idea. It takes all of 30 seconds to spoof.
    People have been compromising voicemail systems without a passkey for years this way.

    Using it as a secondary verification to a (dtmf/tone)passkey would work though.

  4. Coolmod says:

    Why not RFID? Super cheap tags, only those with tags can get in, tag works through the glass…

  5. The hacker Steve Pomeroy, on, has done a similar hack in nature, for unlocking his door with rfid (much more secure than filtering phone numbers if you ask me). The very cool thing with his hack is that he uses the rfid from the transportation cards in Boston (where he lives), which virtually everyone has. He can authorize people just by scanning their cards with his phone. Awesome, isn’t it?

  6. greenbacks says:

    Would it be possible to combine the ultrasonic data transfer to have a mic at the door and play a sound “passcode” to enter?

  7. Daniel says:

    Webcam to read QR codes through the glass ? Printable door keys :-)

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