Are there any locator devices, using sound, for remote controls, car keys, and other personal items?

Answer 1

Yes. Check the Sharper Image for wireless electronic locator

Answer 2

At least cordless phones have a button on the main station that will make the cordless phone beep. Maybe attach it to your remote so you can find the remote....

I also believe that Sharper Image also sold a locator device to attach your keys. If you haven't tried to always place your stuff in the same place, you will lose stuff again and again...