This is what I need... I'm trying to figure a way to trigger an alarm (by way of beeping or vibrating) that will turn on when it is a certain distance (anywhere from 10-30ft, and not with direct line of sight) away from the transmitter. I will need to have one side powered through a usb port and the alarm side powered by a super small battery. This all has to be super, super small for it's application. I know nothing about circuitry or if this is even possible. Is there anything like this?

 

Can you give some idea as to actual desired dimensions and the application?

 

For the size, imagine two sharpie markers sitting side-by-side... That's about the area I have to work with. The lid area would be the alarm and the rest would be the transmitter powered by usb. Basically, the application is just an alarm that let's you know if you've gone more than 15 or 30ft away, reminding you that you left it.

 

check out these devices, small, and battery operated, maybe you can modify the output of the detector to trigger the alarm input >>

http://www.50statesclassifieds.com/product_desc.php?id=25683

The receiver will beep when the child gets further than the set distance, I have one I modified and place in my coffee cup, so when I get too far from it, it lets me know (I hate having to search a 50,000 sq ft building for my coffee when I set it down somewhere and forget ), it has an adjustable range from a few feet to 30.

 

where i can get it?