Finding your keys with Bluetooth

[doragasu]’s wife is always misplacing her keys. To solve this problem, [doragasu] created a small Bluetooth-enabled key fob that is able to remotely sound an alarm when commanded to by a cell phone.

The case and LiPo battery of [doragasu]’s project comes from a small photo frame key fob. The LCD display and PCB of the photo frame were tossed aside for a future project, and the design of the circuit started. The Bluetooth buzzer key fob is based around an MSP430 microcontroller because of their extremely low power requirements.

On the software side of things, [doragasu] built a J2ME app to connect to the key fob and turn the buzzer on. His app is portable to any Android phone, and versions can be ported to Windows, OS X and iOS devices.

How does it work? Well, [doragasu]’s wife sometimes forgets to charge her key fob, rendering the whole project useless. There are ideas for  updating the device to a Bluetooth 4.0 Low Energy device, but no actionable plans. Still, very good work. You can check out [doragasu]’s walkthrough and demo video after the break.

28 thoughts on “Finding your keys with Bluetooth

  1. What about a wireless charger. You could make a key rack that hangs the keychain over a induction charger pad. Put your keys where they belong once or twice a week and then you don’t have to worry about it. Also it would reinforce good practices to keep your keys where they should be.

    1. Good luck getting a wife to put anything in the right spot. I haven’t met a woman who ever guilt the habit of putting things in one place so they wouldn’t be lost. My wife has lost her debit card 5 times in 3 years, among other things.

      @doragasu, if you’re using BT, could you program the module to send a message to the phone when the battery reaches 1/3 power? If it plays the same alert as an SMS message, t’s sure to get her attention.

  2. “But i think getting a new wife will be easier”

    haha, couldn’t help but reminded of borat when he said that!

    Nice new solution to an old idea but as mentioned the battery life is an issue. would love to see a lower power usage chip implemented. Possibly also a kinetically charged device like the watches?

    1. Average power consumption must be about 3 mA. Maybe a solar panel would do the work… if the keys were exposed to the sun. Most of the time they are inside a pocket or a bag…

      1. Put in a shake charger like the shake light. That way, when it’s bouncing around in her pocket it’s charging. or something similar to no-wind mechanical watches.

    2. Didn’t see one in a quick Google search, but I think making one would be pretty simple with a capacitor, diode, coil, and rare-earth magnet.

    1. Good idea, but it would land up being integrated into something like a BMW smart key and be limited to car type/mfg.

  3. Zigbee would work better as far as battery life goes but most “all?” phones lack a zigbee radio so you would need a separate remote.

    1. You said it all, no phones that I know use Zigbee. The phone is the only thing my wife doesn’t loose >_> because when she looses it, she calls herself and finds it.

      Maybe I’ll try to use Bluetooth 4.0 Low Energy when I get a phone that supports it (right now, the iPhone 4S is the only one I know, and I don’t like apples).

  4. Hate to double post but I just thought of a solution to the chargeing problem. Have the buzzer start going off when the power is low as a reminder to recharge. You could also have it send the battery status to the phone and have the phone start making noise when the fobs power is low.

    1. I tought about that, but decided not to implement it because I think it can be nasty. Right now I use one of the lines of the microcontroller to read battery voltage, and when battery is low (about 1/3 charge) what I do is to blink the status LED every 5 secons. Of course the sound should be a lot more effective, but what if for example it starts to beep while you are sleeping? Should I implement also a RTC?

      1. It seems then the path to follow would be an RTC with strategic reminder alerts at a convenient time before the batt dies.

        IE every night at bed time it starts beeping to remind you to charge it.

      2. Zigbee could work if you set it up so that you have plug in bluetooth to Zigbee bridge at your home. Of course it would only work in your home and would be an overly complex solution to the problem.
        You could implement the timed issue in software. Use the phones clock to trigger the phone to check the key fobs battery state. It could check at specific times of the day and say using criteria like is it the phone plugged in.

  5. Why not have it only check for signals every 30 seconds or once per minute… so it’s not always broadcasting… that might significantly increase battery life.

    1. That would not be handy, because of the way Bluetooth works. When using the program, you would trigger a BT timeout while scanning, and would have to do several scans. I’d like to avoid that.

  6. I had a key fob powered by a button cell. You just had to whistle and it beeped. I never measured the range but I think it would be about 10 to 15 meters.

    1. I know that devices, I had one of them maybe 10 years ago (if not more). The one I had was trigged with any loud sound (not only a particular frequency).

    1. The BT module I’m using is the LMX9838 from National Semiconductor (now Texas Instruments). You can find the schematics (detailing of the parts) and source code at my blog. It’s a good module, but difficult to find at a good price.

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