While building the mechanics and tuning the electronics took me longer than expected, the result was really nice: all the hardware neatly fit on the inside of the door, without using screws or nails or anything else that would damage the door. I used gaffer tape to make sure the device stays in place, but that's more a security measure than a neccesity.

The device works quite well, too: I've made a quick movie to show it off. The only problem is that opening the door assumes that you can keep a rythm in your knocks, and unfortunately, the people in the flat where it's installed don't all seem to be musical enough...

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Mark wrote at 20 Feb 2015, 0.27:

At a university that I went to there was an elevator that led to access to nuilding attic the roof of the science building. The roof was a great place to hang out, watch the sunset, drink beer, etc. (I'm sure the Dutch know what etc involves). The elevator required a key to get to the attic/roof and was not to be had. They key turned a switch which triggered the elevator. One night, we removed the panel covering the buttons/key switch, wired a magnetic reed relay to the key switch (with the wires having a plastic clip on them with an official looking wire/circuit number stamped on it) and taped the reed switch to the back of the elevator walls. You just had to stick a magnet to the right place of the elevator wall and voila! Roof access. After 30+ years and a couple of building remodels and elevator refurbs and who knows how many service jobs on the elevator, the magic hack still works!

None wrote at 19 Jan 2014, 12.00:

Check this out: "Miele Knock2open*" dishwashers

Paul wrote at 22 Dec 2013, 20.31:

Wouldn't it have been easier to just lose a key (& 25 euro). But then again they probably didn't want to pay 25 euro for an extra empty room. Might the lock-picking include walking outside on a small rim from the room nextdoor ?

J Sta wrote at 6 Dec 2011, 17.26:

Thats cool, only what if the landlord comes with keys to look inside and sees the whole contraption? You might just force the lock and put in your own, same result, much easier, and you can tell the lord you know nothing about it, make him think he messed up with the keys :)

melndream wrote at 7 Nov 2010, 4.08:

very cool!

paradox wrote at 28 Aug 2010, 6.35:

Nice hack, one way to counter the rhythm of the flat mates is to do the same thing fingerprint security does, and have a close enough is good enough method. I like how you just chuck things together and tinker to make it work

raheel wrote at 8 Aug 2009, 0.49:

wow. thats really cool.. but is it necessary to do this in assembly?. can we do this in C programming?

Amir wrote at 27 Apr 2009, 11.29:

great and Beautiful

MOHD TAHA wrote at 15 Aug 2008, 17.50:


Shaggy wrote at 15 May 2008, 19.30:

I like it. The door looks fairly lightweight - probably some hollow honeycomb. It should be possible to use a magnet and reed switch arrangement, too.

fluxcap wrote at 26 Apr 2008, 6.31:

you should eliminate the knock sensor and use an automotive keyless entry !

rick wrote at 4 Mar 2008, 17.03:

hey i have a question. where can i buy those ATtiny? and can you explain me exactly how to put that firmware on the ATtiny2313? answer me at: rickvanoosterhout@home.nl thnx

tes wrote at 15 Jan 2008, 14.50:


wictro wrote at 13 Jan 2008, 20.30:

Neat-o! i would store all the dirty money, drugs, guns and hookers there ^_^

spazbob wrote at 6 Jan 2008, 1.19:

I agree with troy.

troy wrote at 20 Dec 2007, 23.14:

wow theres alot of resentment in the comentary here. i dont understand why people would come to view this if they dont agree on it, much less comment. it takes less effort saying nothing than that of getting mad aobut it. just appreciate the technology that these people have created. i really dont see any of the ass holes who condesendingly comment on this page with any cool hack ideas.

lewis wrote at 15 Nov 2007, 10.53:

If there's a gap, instead of knocks use an IR detector and a TV remote. Won't have to worry about keeping tune then.

Taehl wrote at 15 Sep 2007, 6.11:

Beautiful. Truly.

madhujo wrote at 30 Aug 2007, 12.20:

I like it but,what happens if the owner of the house opens lock with his key. it's cool project with which we can develop new ideas..

yuri wrote at 14 Aug 2007, 2.43:

=) i want one of these :'(

Observer2007 wrote at 18 Jul 2007, 16.45:

I think you should read Ronnie's note of 15 Jun 2007, 11.55 and Markuslarkus' note of 15 Jun 2007, 5.40.

ravn wrote at 18 Jul 2007, 15.20:

It would be really nifty to build this into the doorframe, so that it isn't visible from either side. When you remove and disassemble the lock insert you will find that there is plenty of unused space. It might be possible to insert the electronics and a small, slow motor with a good transmission ratio into the metal casing while keeping the original cylinder of the lock.

yellowjacket87 wrote at 18 Jul 2007, 2.04:

Dude you should make those and sell them

ryan wrote at 17 Jul 2007, 23.11:

Very cool hack, but would think it would be much more practical just to spend your energy making a key?

:derp: wrote at 10 Jul 2007, 13.16:

Nice, I'll keep something like that in mind. Might build one into my new bedroom door, after I break this old one.

vor wrote at 19 Jun 2007, 22.16:

There is also a kit for autos when you forget your key - or want a keyless entry http://www.knockinkey.com.au

jordan314 wrote at 15 Jun 2007, 19.00:

Brilliant! I've always wanted to do this with RFID, which I think would be more secure, but you've provided a schematic with printer motors and rubber bands for it to happen. Thanks!

Pdg wrote at 15 Jun 2007, 16.01:

I think there is a problem with transistor T2

meneer wrote at 15 Jun 2007, 15.42:

What happens when the landlord comes and opens the door with his key? Who will get kicked out of his apartment then? (Hint: you) Nice hack though.

ronnie wrote at 15 Jun 2007, 11.55:

Cool hack, but not very legal. If the landlord has reason to lock the space, it's not yours to open. If you think it's no big deal, why not ask the landlord to rent the space for a few bucks extra?

cooperised wrote at 15 Jun 2007, 10.18:

Nice work! The whole T2 being upside-down thing... it's working as an emitter follower into a high-impedance load so it won't make much difference (transistors are notionally symmetrical [NPN], but messed with so they have a higher current gain when connected 'correctly')...

me wrote at 15 Jun 2007, 10.04:

Nice hack again. I'd consider using protection diodes across the FETs/coils, though - to protect the FETs from the backfiring induction spikes.

markuslarkus wrote at 15 Jun 2007, 5.40:

"but closing an empty room for no apparent reason isn't really ethical too, in my opinion" Sorry, but that's so idiotic and juvenile I can't really get past it to your circuit. Maybe when you're old enough to own some property of your own you'll have a different opinion.

the White Rabbit wrote at 15 Jun 2007, 2.02:

how fucking cool is that, hugh?! would be nice to see is winding from the other side, like boob and rob already noticed. nice work, so far.

Rob wrote at 14 Jun 2007, 5.48:

I would like to see the video from the rear to show it all moving.

boob wrote at 14 Jun 2007, 3.41:

I doubt it. If you're so smart how come we can't see it in action.

BigStig wrote at 13 Jun 2007, 15.17:

As an EE I 1) think that's the best schematic I've ever seen & that's mostly becuase of the tm'd software name & 2) I appreciate the use of tape in electronics projects, it's a must.

Black Coffin-san wrote at 13 Jun 2007, 14.22:

pretty crude, but nice enough.. very resourceful, and.. uhh.. hey how the hell were you able to program in assembly? It's a bad thing's there's no such things like that at our area.. xD

Jon wrote at 12 Jun 2007, 23.33:

That's off the fucking chain!! Nice work.

Keehun wrote at 12 Jun 2007, 22.50:

Nice work.

Jason wrote at 12 Jun 2007, 20.47:

Hope the Landlord dont call the bombsquad ;) nice work

shuma wrote at 12 Jun 2007, 17.24:

It may not be a first but it does make the task of building this device seem much more doable. Definitely a nice thing to have around. I'll keep it in mind for my dorm room.

Locksmith wrote at 12 Jun 2007, 14.47:

Neat, but not a first. http://www.nokey.com/knocknoctoac.html http://www.knocknlock.com/ http://www.isracast.com/Articles/Article.aspx?ID=3

MrRandomPerson wrote at 12 Jun 2007, 9.55:

Really nice idea! you should post up a set of instructions on how to make something like this!

schraitle wrote at 12 Jun 2007, 5.32:

I actually had an idea similar to this which would use a remote control, the schematic you have will help me out immensely, thank you, very nice work

psycodrew wrote at 11 Jun 2007, 22.18:

(00| 1 w0u|d ju57 u53 4 P1( 8u7 571|| (00| hey how about you try putting the chip in the case and extending the button out with one of those radio shack ones that screw in the cas3

eMpTy wrote at 11 Jun 2007, 21.16:

Wlol, I'm gonna brute my front door 4 this!

MadCatMk2 wrote at 11 Jun 2007, 20.53:

omfg, cool, lol ;)

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