The USB-based door lock

The USB-based door lock

The USB door lock might look crufty, but the next time you forget your keys but still have your iPod you'll wish you'd built one.

If you're looking for a clever way of keeping your kid sister out of your room, how about a deadbolt that unlocks when you insert a specific USB key?

Hack a Day are currently showing off the work of the Makers Local 256, who have built a mechanical deadbolt system that relies on a certain USB device being inserted before the lock is released. Where it gets clever is that the system will work with any USB device – similar systems rely on storing a 'key file' on a USB-presented mass storage device. Basically, you can unlock your door with a mouse, a keyboard, an MP3 player – anything with a USB interface.

The way the system works is for a host PC to read the unique serial number of a given USB device. Every USB object has one, and – in theory, at least – it's unique to that individual device and is never duplicated, even amongst devices of the same model. The PC then compares this unique serial number to those stored in a flat-file database – if it matches, an unlock instruction is sent to a USB-connected microcontroller, which triggers a servo to withdraw the bolt and allow entry.

If that all sounds a bit confusing, there's a neat video demonstrating the concept of the system and showing the unit in action.

While it's not exactly the prettiest hack in existence – being built into a plastic box the team jokingly refers to as “transparent aluminium” – it's certainly a neat trick, and speaking as an individual who is constantly losing his keys but always has a USB pendrive about his person I can certainly see a practical use for the system.

If you're tempted to implement your own version, the site has instructions and diagrams along with the source code you'll need both to read the USB ID and to interface with the Freeduino microcontroller. The parts for the project can be purchased for around $60 (£37) – obviously discounting the PC needed to power the system.

Fancy a unique locking system for your pad, or would you prefer something with more of a biometrics flavour – or perhaps good old keys are enough for you? Share your thoughts over in the forums.


Discuss in the forums Reply
shigllgetcha 23rd October 2008, 17:17 Quote
you could use your phone/ipod with the right lead
Veles 23rd October 2008, 17:30 Quote
not very good when there's a power cut, but it's still a cool idea
mrb_no1 23rd October 2008, 17:37 Quote
Originally Posted by Veles
not very good when there's a power cut, but it's still a cool idea

just get an uninteruptable power supply and that should solve that problem. i like the idea and might try it, just for the heck of it.


Vigfus 23rd October 2008, 18:33 Quote
Cool. :)

If i'd still be working at the school this would be neat. I could use the override to unlock the door whenever someone knocked on the door and i would be able to show off to the geeky students by opening the door without a key. ;)

I guess it could be operated via the network too. The possibilities are endless...
shigllgetcha 23rd October 2008, 19:22 Quote
bluetooth door opener would be cool. just leave the bluetooth on in your phone and when u walk up it unlocks
mclean007 23rd October 2008, 20:07 Quote
Yemerich 23rd October 2008, 21:21 Quote
Originally Posted by mclean007

My thoughts exactly...

I will make a system that all you need will be a finger. Press a buttom and it will open. Cool, huh?
modgodtanvir 23rd October 2008, 21:26 Quote
Not a bad idea... though I suppose it works on the same principal as any other form of electronic identification...

My concern is durability, the USB connector isn't the strongest thing in the world, and even through irregular use I have managed to bend and break a good few... if somebody puts any force on it while it is connected, or has to put it in at an awkward angle, I can see it quickly wearing down...
Woodstock 23rd October 2008, 22:01 Quote
I like it, dont think it will ge a good idea to keep a spare usb drive under the door mat thou. Think it would be a lot better with (as mentioned before) bluetooth or rfid or something like that, or an actual use for a biometric scanners. Right im going to stop now, as the landlord would kill me if i tried to implement any lock like that
woodshop 24th October 2008, 00:07 Quote
replace the microcontroller and the PC with a gumstick.
Fused 24th October 2008, 01:13 Quote
In the end can anything really beat a physical key? I like the bluetooth idea but would it ever be secure enough?
BentAnat 24th October 2008, 06:23 Quote
Hm. Build some custom circuits, and one could prolly run something like that without the Host PC, and off a Battery of sorts...
And if it's small enough, one could use something like that to, say, boot up a PC...
Brooxy 24th October 2008, 10:26 Quote
Kinda pointless, but with the modding spirit of 'because I can' it's also kinda cool
_DTM2000_ 24th October 2008, 10:55 Quote
This does seem a little pointless. There are tons of different door access control systems available that use more suitable key replacements than a USB device. I just think something like a swipe card, RFID proximity token or finger print is a more suitable key but I guess these have all been done before. As a proof of concept, the rest of the design is more useful and I'd certainly be interested in trying this out with a different form of access token.
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