I found this at walmart for a dollar. web page clegg For emergencies, what do you think?
I didn't figure out how to post a picture, but it is on the web page.

Very cool idea, great price, but I have my doubts about it for several reasons.

I doubt it is nearly as loud as a Fox40 whistle.

The red LED light is not nearly as useful for my family, several have a very hard time seeing the deep red colors, and they even give my mom a headache. In fact, I have found that it takes such a bright red to be able to make out details that it destroys my night vision more than a white light of brightness minimal to use for the same purpose. Green, yellow or white would be much more useful to me overall than a red.

I do not know what batteries it uses or if they are replaceable, nor do I know how durable the item is, but for a buck it would be worth it to try one out.

I haven't really used mine but I thought it might be useful for signalling (I teach shop) but one thing is, the chain is very weak and broke already, (2 weeks old)

Thanks for the info, hillbilly and grommit! I was looking at something like this for a school-wide safety project, but I don't know if I want to spend the $$$$ on something that won't survive dangling from a backpack more than a couple of weeks.