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[How-To] Keychain detector


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#1 Dan (electron)

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Posted 13 October 2008 - 08:09 PM

Keychain detector
by electron

For a while now, I have been trying to figure out how to detect when the wife is at home, or 'on the road'. I needed something that was fairly accurate, and inexpensive as I was planning on triggering home automation functions based on this 'occupancy' status. For various reasons, I could not rely on the car occupancy detection method, and other solutions were too costly or not accurate enough. The solution? Detect when my wife is home by looking for the presence of her keys on the keychain storage hook located in our kitchen. She will never leave the house without her keys, so this was the best methodology to use as an occupancy sensor. Most people always have their keys on them, and usually place them in the same location when at home.

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Concept
There probably is no simpler solution than this one. Think of a simple door/window contact, but the magnet/sensor combination are replaced with two metallic eye hooks. When a metal keyring is placed on these two hooks, it will close a circuit between them, and trigger an 'alarm' just like a regular door/window contact would.

Build it yourself

Step 1
Find two metallic hooks or nails which can hold the weight of your keys. It is up to you on the aesthetic details (keep the WAF in mind though). I used an existing key hanger board, and simply added 2 brass eye hooks to the bottom. It is important that these hooks/nails are conductive, so when in doubt, make sure you use your multimeter to confirm their conductivity (using the resistance settings of your multimeter). You could also wrap the leads from a wireless door sensor (i.e., DS10A) around each hook, and touch one hook with the other. If the light blinks, you know you are all ready for the next step.

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Step 2
Decide how you want to interface this 'sensor'. There are many ways of doing this, such as using a spare pair in your Cat5/phone wire, wireless alarm sensor such as the GE wireless sensors, or in my case, a spare X10 DS10A. These sensors are very inexpensive, and their status can be monitored by my Elk M1 alarm panel (using the W800RF32 wireless receiver).

I disconnected the wires leading to the magnet, by undoing the 2 small screws, and pulling the wires out.

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Step 3
Install the hooks, and connect them to the sensor wires. Since I am using the typical brass eye hooks you can find at any store, I predrilled 2 holes, about .5" apart. Since these hooks have to be screwed in, make sure you have enough clearance so they can turn! Also make sure that the holes are drilled as straight as possible (use a drill press if you have one), or it will look strange, and might cause false positives if the hooks aren't aligned.

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I stripped approximately one half inch of insulation from the DS10A wires, and inserted them carefully into the holes. While holding the wire there, I carefully screwed the hooks into the wood. This seems to create a very solid connection, so there is no need for soldering.

Step 4
Last but not least, configure your sensor if needed, and make sure your home automation system sees the on / off signals by hanging your keyring on the hook. If everything works, then mount the key hanger and start programming. Make sure that other keys won't obstruct the hooks, as you don't want to generate false positives.

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What's next?
When the wife isn't home, the system knows, and forwards any important reminders/notifications to her cellphone. Please keep in mind that certain applications might require the use of a timer (in case your keys get bumped when someone else hangs up their keys). There are other interesting things you can do (e.g., announce new messages when you arrive home), but there are too many to list here. While some might wonder if it is worth it, think of how inexpensive and easy this method is (especially when compared to RFID solutions), and if everyone in your household puts their keys on the hook when home (and many do, I have asked around), the benefits can be huge.

If you have any suggestions, or comments regarding this article, please don't hesitate to share!

#2 Snypez

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Posted 13 October 2008 - 11:01 PM

haha, I love your idea! I was just talking to my colleague about doing this, and then I logged in and saw this :(

Now I just need to talk my wife into hanging her keys in the same spot!

You might want to revise your design a little. Over the years, the keys may scratch up your cabinet. It looks like your keys are away from the wood, but sometimes peoples fingernails (when they grab the keys) can scratch up the cabinets as well.

#3 Dan (electron)

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Posted 14 October 2008 - 06:43 AM

Snypez, you bring up a good point. My wife and I had this discussion as well, so I am planning on designing a new board soon. This board was a proof of concept, which ended up doing the job really well.

#4 Squintz

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Posted 14 October 2008 - 07:23 AM

This is why I love this site. It's the creative ideas like this that make it so valuable.

When I first saw the picture I thought you might be using some sort of microswitch that activated with the weight of the keys. But this is much simpler and if you were building a new house you could even hardwire this to an Elk M1G or similar and avoid the unsightly DS10A.

Good Job

#5 Dan (electron)

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Posted 14 October 2008 - 08:05 AM

Thanks Squintz. I actually have access to a Cat5 run, which is within inches from that location. If the location was more visible, I would probably hardwire it, or use the much smaller GE wireless security sensors. You could also embed the DS10A in the board itself as well, but since this is only a temporary solution, I just mounted the DS10A with velcro next to the board.

#6 TeleFragger

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Posted 14 October 2008 - 08:08 AM

Now I just need to talk my wife into hanging her keys in the same spot!



I thought I was the only one with that problem!!!!!

wife couldnt find her keys last night to go to college.... well they were in the bottomless pit... her pocketbook!!!!!!!1 :(

#7 DeLicious

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Posted 14 October 2008 - 09:05 AM

trust me... whatever problem you have with your wife, you're not the only one. there's always another ;)

#8 opie

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Posted 14 October 2008 - 09:26 AM

trust me... whatever problem you have with your wife, you're not the only one. there's always another ;)


Add me the the list of those with spouses that don't know where their keys are. Maybe this would be a good incentive for her to place her keys there. I could have the house warm up a little more when she gets home (she's always cold).

#9 BraveSirRobbin

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Posted 14 October 2008 - 09:57 AM

Other possibilities:

Hang the dog leash in the same spot and determine if the dog was walked that day

We have a lock box for our mail so you can hang the mailbox key in the same place and know if someone checked it that day.

#10 Dan (electron)

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Posted 14 October 2008 - 10:05 AM

Very good ideas!

#11 drozwood90

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Posted 14 October 2008 - 11:43 AM

I saw something like this a while ago. Nice spin on it!

What the other site did, was pump the triggers into an I/O board, instead of a DS10A...and he used 3.5mm headphone plugs. He put one on each set of keys...then the user had to PLUG the keys into the unit, instead of hang them.

The only advantage is you will always make contact (my wife has plastic things on her keys he might use to hang the keys with).

The disadvantage is you need to "teach" each person that they need to use the plug.

What's nice about your setup is you could also have a guest hook...but that only really works if the guest uses a hook at their house.

I've been thinking about something like this, but with weight, as my wife keeps her keys in her purse...

Then I found cheaper RFID and started to play with that stuff...so I don't know which way I'll go...GREAT idea!!!

--Dan

#12 jwilson56

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Posted 14 October 2008 - 12:11 PM

I can see your wives wrapping a bare wire between those two hooks and skipping out to the shopping mall all day with the plastic.. hahahaha


"Oh sure I was home all day slaving over this house"

#13 Lagerhead

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Posted 14 October 2008 - 06:49 PM

I can see your wives wrapping a bare wire between those two hooks . . .


Whose wife knows enough to figure this out? ;) Not mine. ;)

#14 jwilson56

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Posted 14 October 2008 - 06:57 PM

We have been married 30 years... she would know enough... lol

#15 Work2Play

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Posted 14 October 2008 - 08:09 PM

Mine keeps asking how I know what she was doing all day... She hasn't quite figured out that a lot of times I have ElkRM up at the office, so I see the motion and door activity (as a side effect). Yesterday she wanted to surprise me by doing some of the painting, so when I called a few hours later and asked how the painting went, she tried to play it off... but I could tell what she was doing by what doors and windows were open...

She was a little irrirated the other day when she called from the car (you can tell from the hands free), and hadn't armed the alarm, so I armed it on her. She came in with her hands full, not expecting to have to deal with it...




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