Hello, they already make things like this child guardian alarm which can be found at this sight. Consists of a key fob, you hang on to, a receiver unit which can be paged and which will make a sound when you push the button on the keyfob and it comes with a small fanny pack to house all in. Sounds like it would be the ticket. I use this to keep up with my kid in the park and so on. If it is too loud... There's always wrapping in a sock or something and duc tape.
http://www.familydefense.com/childguard.htm [Non-text portions of this message have been removed]
