Ahoy everyone. So this is something I've looked into for about the past year. My plan was to begin the project immediately after Christmas, but since the hackspace got started, I figured that we as a group could come up with a better design than my own.
My initial desire for this project was to implement subcutaneous RFID implants for me and close family who may wish to come visit my house. Through a veterinarian friend I got my hands on the proper RFID chip and equipment to inject myself. However, this plan has now been vetoed by my fiancée. So instead I decided I wanted an RFID tag that could be read as soon as I reached the top of the stairs to my house. I don't like the idea of having to swipe anything (what if my hands are full of groceries?). This would mean the reader should be capable of reading a tag from a distance of about 3 feet, mayyyybe 4 feet. This introduces us to our first problem:
1.) RFID tags are balls for being detected at long distances. At DEFCON 18 this year, I got to witness a demonstration of a high gain, high power antennae that could read a conference halls worth of RFID tags (the ones that are printed on stickers and are in long narrow strips about 2 inches long). However, the antennae's were HUGE, and the power required as sick. Why do you think stores use such large theft detectors at the entrance and exist to their stores? As far as I know, this is because the large devices act as antennae's to scan everything you're carrying. This leads us to two possible solutions:
1a.) Use a high gain antennae, possibly embedded into the siding of the house or railing around my step? This seems rather implausible.
1b.) Use something other than RFID. I really like the idea of RFID due to the abundance of low cost parts and extensive knowledge base on the internet regarding this topic. Does anyone know of any other solutions (other than using active tags)? I'd love to hear them! I will resort to an active tag if I have to, I just would prefer not to go that route. My original plan was to use my arduino in combination with a parrallax RFID antennae (http://www.instructables.com/id/AVRArduino-RFID-Reader-with-UART-Code-in-C/
). There is lots of code for this and would be trivial to implement.
2.) What kind of door locking mechanism do I use? Hackaday had a keypad doorlock like the kind you can buy from home depot (there is a key pad above the handle that you enter a code into, and it unlocks the door). You can take the back panel off and wire in your own mechanism for triggering the door lock. My mechanism would be the arduino triggering this door lock. However,this would look rather ugly I believe. I would have to likely mount it on the door, but then how would it be powered? A very low power wireless chip (XBee?) could maybe run off a battery and listen for a signal sent from the arduino, but again, what if the battery dies while I'm away? Another solution exists:
2a.) An electronic door strike. This type of lock has a chunk of metal that falls into a hole cut in the door itself and latches. When power is applied, the lock is retracted to unlock the door. This is an elegant solution as it doesn't depend on the power being on to lock the door. Also, the arduino system could reside in or mounted on the wall near the door frame and control this mechanism from there. Any time someone approaches the door within 4 feet, the door would unlock, meaning you wouldn't have to rely on locking or unlocking your doors ever!
I have links to a lot of the equipment that I had in mind and can post them if necessary. I want to hear your ideas! This project is purely for my house but could be adapted for most other homes if need be. Hopefully it can act as a prototype for the security at the hackspace itself. The hackspace will have different requirements, but I think that it would in effect be similar.