is there a low cost gadget that could be used as wearable motion detector / people counter?

[code_grey]

let's say this gadget would be attached to your back or the back of your hat and would detect either people standing or people moving within some radius. Just enough of a radius for you to turn around to say hello :-) For now let's ignore the question of how to interface the signal with the user.

Do they nowadays sell "cheap enough" gadgets that could be adapted for this? Googling for wearable motion sensor is bringing back research papers on stuff I don't even fully understand (spying on patients and the elderly? not sure). Well, so even if nobody is selling this specifically, maybe there are dual-use gadgets that could be used directly or after modification?

E.g. I think there is some elaborate (and probably expensive) motion detector in XBox or something of that nature - could that be made wearable? Or is it too heavy?

[Fear Itself]

I'm no engineer, but I would think attaching a motion detector to a moving object would be problematic.

[beowulff]

I’m pretty sure i could design an ultrasonic person detector that would be the size of a lighter, or smaller.

[Fubaya]

You don't want a motion detector, you want a proximity sensor. It looks like there are some for sale online, but who knows if they're any good.

What immediately came to my mind is that the rear bumpers of many modern cars have several sensors that make something in the car beep when they detect something close so you don't run into anything. The sensors themselves are small, about the diameter of nickel and an 1-1.5 inches long. I don't know if any computer power is required but I doubt it. You'd probably just need a power source and a way to turn the signal coming from the sensor into something you can use.

[code_grey]

Fubaya, and what would be the range of a low key proximity sensor? After all, I don't want to turn around to say hi to a person who is already immediately behind my back.

Also, can they measure the velocity of the object, at least crudely?

[code_grey]

well, and how about the video cameras? I understand that a web cam is too big, but then the quality needed here seems much lower than what is provided by a web cam. Could a video camera be significantly miniaturized, trading off image quality for size and cost?

Or basically the answer is "yes", but it will need to be designed from scratch rather than bought off-the-shelf?

[Fubaya]

Originally Posted by code_grey

Fubaya, and what would be the range of a low key proximity sensor? After all, I don't want to turn around to say hi to a person who is already immediately behind my back.

Also, can they measure the velocity of the object, at least crudely?

I really have no idea. The only ones I've used are the ones in a vehicle and their range is probably 5 feet, maybe 10 max. They're not really designed to detect velocity, but you can sort of tell. They start beeping a few feet from an object and beep faster as you get closer. Of course, it's all relative and the same things happens if an object is moving toward you. They probably send out an electromagnetic wave and beep if it gets returned. If something is close, it returns faster and beeps faster. So "beep...beep...beep..beep..beep.beep.beep.beepbeepbeep" is one velocity and "beep...beep.beepbeepbeep" is another.

Originally Posted by code_grey

well, and how about the video cameras? I understand that a web cam is too big, but then the quality needed here seems much lower than what is provided by a web cam. Could a video camera be significantly miniaturized, trading off image quality for size and cost?

Or basically the answer is "yes", but it will need to be designed from scratch rather than bought off-the-shelf?

There are a lot of tiny cameras out there these days. My cell phone has a pretty decent camera and can record video at 720p HD. Watch a hidden camera show on TV and they label the video as coming from "glasses cam" or "lapel cam." You can get little cameras like this and wire it to whatever you want to use to receive the video. I don't know if exactly what you want can be bought off the shelf, but the components probably can be.

[JFLuvly]

You could stick this behind your ear

http://www.spyshops.com/cgi-bin/shop...n&key=WHCMPENC

Forgot to mention that there are all kinds of other types on that site alone, there are many more on the web.

[JFLuvly]

You can watch on these

http://www.vuzix.com/consumer/products_wrap920.html