Ever get the feeling that your door is unlocked?

  1. Hey guys!

    I've just thought of a neat idea for a summer project, and I'm requesting some opinions on its usefulness and feasibility.

    For a forgetful guy like me, I always get the feeling (while I'm walking on the streets) that my door is unlocked. So today I was thinking about how to make a device that checks if your door is locked or not. After a minute or so, I thought of a basic design: An accelerometer that is connected to a wireless transmitter (since most doors are deadbolts and require turning the lock to different orientations to lock them). This way, all you would have to do is to stick a non-intrusive modified accelerometer onto your lock!

    So what do you guys think? Possible issues (Range problem)? Possible solutions to possible issues (making the signal send to a wifi network and uploading the status of your door online)? Ways to design such a device?
  2. jcsd
  3. Bear in mind the different motions you could potentially need measure. If it's a deadbolt moving in translation, will an accelerometer tell you anything about its position when not in motion? If it's a handle or lock barrel rotating into position, actuating the bolt, can you use a bi-axial (or tri-axial, they're not significantly more expensive) accelerometer or gyroscope to measure the rotation instead?

    Also, before you go that far, you could try thinking about more simple sensors. Tilt switches and limit switches (especially) spring to mind. A binary sensor which tells you whether your door is locked or not depending on whether the deadbolt has travelled past a switch would be a very simple solution. Not sure you'd want your house's security resting on it though ;)

    Finally, there are a number of solutions to access your sensor state remotely. Some make little sense (as you suggested, the range problem) but updating a status via the internet is probably a feasible option. For instance, I write pieces of software that run via a webserver, which I can log on to remotely regardless of connection method to check on the status of my experiments.

    Try looking at LabVIEW and running a webserver through that. It's a pretty simple way of achieving what you're after without too much need of coding experience too.
  4. FredGarvin

    FredGarvin 5,084
    Science Advisor

    You non't need accelerometers. Although, that idea is being used by a sensor I have on my garage door. It signals a receiver in the house to light a red or green light depending on the position of the door.

    Simple contacts or limit switches are all you need.
  5. Great suggestions! But the reason I wanted to use an accelerometer was because it is easy to attach and very non-intrusive. One of my goals for this device is for it to be as simple to install and make as possible. What could I use if not an accelerometer?
  6. Danger

    Danger 9,663
    Gold Member

    Might I suggest medicinal treatment for your OCD?
    This is not a flippant response. I have a touch of compulsion as a nasty tag-along to my ADD, and the medication helps a lot.
    I am not a medical professional, and even if I were we do not advocate any form of treatment on PF. I merely suggest that perhaps you could consult your physician to investigate whether or not this particular worry of yours is a symptom of a psychological condition. (Even with my meds, I still check my pockets at least 3 times before I leave the house to make sure that I have my keys to get back in.)
  7. minger

    minger 1,498
    Science Advisor

    I'm similar although I don't consider it to be OCD. I associate that with people who wash their hands 40 times a day and need to take 12 steps from the couch to the bathroom.

    I simply like to make sure that my door is locked, that's about all. It probably stems from getting robbed twice in college, but because of that, I consider it a worthy cause to check the doors when I up in the middle of the night going potty.
  8. Danger

    Danger 9,663
    Gold Member

    But once clear of the house, your worry is left behind? That is where I see a difference.
  9. minger

    minger 1,498
    Science Advisor

    I'm usually not too concerned when I'm away from the house. It's when I'm in the house that I'm concerned. I'm concerned for what a criminal could do to me or my room mates, or what I would do to them.
  10. Danger

    Danger 9,663
    Gold Member

    That's simply common sense. Just make sure that you put more concern toward what they might do to you than what you might do to them. When in doubt, go for the pre-emptive strike. As I always say, I'd rather spend the rest of my life in jail than the rest of forever dead. (This is based upon the assumption that you are very good with whatever your weapons of choice are. If you aren't, then hide somewhere and call 911. That should be your first action anyhow, as long as you have time and access to a phone.)
  11. Lol. Gentlemen. Whatever is this discussion going? This is the engineering and design forum is it not? I am just looking for some ideas and some inspiration for what I think is a worthwhile project.
  12. turbo

    turbo 7,063
    Gold Member

    Might I suggest something a bit simpler? How about a contact switch or similar and a short-range signal to a key-fob or similar? You set the lock as you are leaving, and later when you start to doubt yourself, you check the fob on your key-chain to see if the red (locked) LED is illuminated or if the green (unlocked) LED is illuminated. No problems with range, timing, etc. Latch that sucker and get some peace of mind.

    BTW, if you sell this idea to Ron Popiel, and don't cut me in, I will hunt you down like a dog.
    Last edited: Feb 11, 2010
  13. Have a simple switch on the inside of the door frame where the dead bolt enters. When the deadbolt is locked, or pushed into position, it will depress a button, which would in turn update a twitter status, telling you that your door is locked. You could set it up to update say every hour or so.
  14. Danger

    Danger 9,663
    Gold Member

    Sorry, Inutard. I owned a security company for 17 years, so I tend toward maximum survival of the client. I didn't realize that you had a specific electronic plan in mind. :redface:
  15. berkeman

    Staff: Mentor

    Another approach would fall under the KISS principle. Figure out a routine where you basically have to lock the door to be able to leave. Something as simple as hanging the keys on the deadbolt knob inside the door, and making a point of taking the keys off the knob and locking the door right as you leave. Then put the keys in a pocket (or on one of those handy belt snap hooks that I started using a while back), and make a point of patting the keys as you start walking away from the door.

    Or something similar. For example, there are disk brake locks that some motorcyclists use to lock up their front wheel so their bike can't be "roll-away" stolen. Problem is that it is pretty easy to forget that you have locked your front wheel, and there is a risk that you will get on your bike and try to ride away. It's not a very long ride. Not that it's happened to me or anything; I'm just saying. So a very clever solution is offered as an after market addition to disk locks -- it's a bright orange coily cord thing that runs from the disk lock up to the ignition keyhole. You have to remove the keyhole end to start the bike, and that's your visual reminder to remove the disk lock. Remove before flight!
  16. I like that idea. Just like the wallet problem, where no matter how sure I am I have my wallet, I will always check that it is there every 10 minutes or so. Same principle as the key idea, or the orange coily cord.
  17. Danger

    Danger 9,663
    Gold Member

    Cool idea, Berkeman.
    It's sort of like why I have the chuck key for my electric drill fastened to the plug end of the power cord; I have to unplug the thing before changing bits. It's a pain in the ***, but it's probably saved me from a lot of injuries.
  18. Lol danger its ok. I forgive you :)

    @turbo-1 I also thought of that idea. But think i started wondering what would happen if i forgot to set the switch... Lol (Set it and Forget It!). But i do like the immediate signalling to the fob tho. If i keep the accelerometer, i can just have it immediately signal some indicator on my keychain when i lock the door from the outside! That would eliminate the range problem =P

    @MotoH How hard would that switch be to install though?

    @berkeman Yeah I was doing something similar to that. But sometimes I lose my cord... :(
    Last edited: Feb 13, 2010
  19. Well I am not an engineer of any sort, but drilling a hole on the inside of the door frame so the small switch fits, which can be extremely small, because all they have to do is complete a circuit. Run the wires from there to a module that can connect to a computer and run a specific set of operations (this is where it gets fuzzy because I am definitely not a programmer!) But I have seen homemade devices that update to twitter before, so it shouldn't be that expensive or technical.
  20. Why not just use commercial locks that ALWAYS lock from the outside(without a key) but from the inside you can simply turn the knob/handle/etc and get out?
    Very available. Problem solved. Sleep tight. ZZZZzzzzzzzzz
  21. Simply because I would have to change my lock and that would constitute as an 'intrusive' change that requires more effort. Besides, this is a summer project of mine, so just changing the lock wouldnt do it for me.
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