How to make a key beeper that can be activated by a cell phone?

Is there a device that that can be somehow activated by 'some' signal produces by today's cell phones (bluetooth, wifi, infra...) and then make a beep sound? Preferably it should be small, light, cheap, with low consumption of energy.

It should work as a beeper to find a thing that it is attached to more quickly.

Any ideas?

well you would need a cellphone, wifi , bluetooth or whatever mode you want to use tranceiver unit connected to it so that it could receive the appropriate signal. that box of tricks could end up being many times bigger than the item its connected to eg. a keychain.

years ago keychain beepers were very popular, all you had to do was whistle/handclap and it would beep back at you when it was within range of your whistle/handclap :) They were dreadfully hard on batteries tho :(

Dave

Yes, what I want it to make is basically the same thing as a keychan beeper. However, instead of that device which you use to acitivate the beeper, I want to use a mobile phone.

I am just thinking about it and all it boils down to questions like:

How difficult it would be to put it all together?

What kind of connection would be optimal. - I know that bluetooth needs to pair with the other device. I think that'd be to much overhead. Because the beeper doesn't need to send any signal, it'd be enought if it only received the signal and react.

How expensive it would be?

I am just looking for any advice or ideas ?

well a cellphone or bluetooth both rely on 2 way comms
another alternative would be to use the 433MHz sender/receiver pair of units an easy single way comms with coded control

Dave