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My wife lost her keys, I'm hacking a key pager together. It's working . . . sorta. Answered

I was thinking: 1)An old cordless phone with a pager function I could hack apart and reuse. 2)An old cellphone for the same purpose. 3)A crystal radio learning kit. My goal is to do this for under $40--the cost of buying that way overpriced pager system you've seen advertised--and for me to learn while doing this. After reading another instructable, I was inspired to use a cheap radio controlled car.



11 years ago

This is strictly a visual device so it may not suit your needs but it's a neat idea anyway. See http://devan.sensoryengineering.net or search for "LED marker beacon". This circuit uses a blinking LED plus a couple of othe components and turns itself on after dark. It looks to be small enough to put on a keychain.

Yeah, that's probably not really going to work for my wife. Actually, I received a sample self-driving beeper in the mail last Thursday. I hooked it together and got it working and then fried it with ESD by not being careful. I'm a bit depressed about that.

Okay, I've kind of got this thing working. I reverse engineered an RC car receiver and figured out a good point to hook up a piezo speaker. The transmitter is in the 27Mhz band, but I had a hunch that there might be a lower frequency harmonic that the piezo would respond to. I hooked up the piezo, and sure enough, there was a faint beeping. Great! That's some progress. However, I need a LOUD beeping for this to be a useful key finder. In the first picture, the parts in red show how I hooked up the piezo speaker. It occured to me that maybe I could amplify the signal with a transistor and that would mean a louder beep. So I tried to hook up a transistor as seen in picture 2. That didn't work at all. Not even a faint beep. Now I'm stumped. Anybody have a simple idea of what I could do to make the beeping of the piezo louder or what I'm doing wrong here?


I too have looked around for a device that I can bult like this but can't find plans. Any ideas?

at this point I think I'm going to try to chop up an old RC car.

My parents have the same problem with keys, remotes, etc. etc.

It totally goes against a personal sense of DIY and personal experience.... Over the holidays, not able to figure out what to get for my mother, I came across an 8 device pager thingermabob. It was the first, and likely last item I bought from The Sharper Image. My mother is the hardest person to give a gift to (the right type of course) -- and that's a capitol HARD.

The cost was $50 (shhh don't tell her) and she probably uses it 7 times a week. So at 5 minutes saved per use - that's over 30 hours a year! So even at minimum wage - it pays for itself quickly...

So from my experience with this, I'll give it a high score because it does 8 times more devices than what I would have made -- and it won't eat batteries like something I would have made :/

I know it doesn't help on how to make one... I'm just sharing our experience ;)

Well it's good to know the thing isn't a rip-off . . . but I'm still making my own. I want to learn, for one thing. And, um, $50 is still a lot of money. Besides, I only need one for her set of keys. Thanks for the memories, though :) Any idea which source might work better than another?