Harbour Freight has a tubular aluminum whistle that is like $1 on sale and attaches nicely to a keychain. I got one for my wife a couple years ago. It is still doing fine.

I see something similar on eBay for under $1 shipped on a regular basis.
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Warning - I am not an expert on anything having to do with this forum, but that won't stop me from saying what I think. smile

Bob