Let me go completely OFF TOPIC here.

Why exactly do you need a whistle? The chances are, if you have an emergency in an urban area, then you can just call for help. The main reason why you might not want to do that - is because SOME of the people in your area are NOT friendly. In which case, a whistle isn't much help.

A cell phone is a much better signaling device. Because you can get a message directly to people who CAN come and look for you. But the main problem with phones is that signal reception can be poor. THEREFORE, what you really need is a portable antenna for a cell phone that BOOSTS the signal strength.

It seems to me that this choice might be a LOT more useful in an urban situation. I need to do the same thing myself - get some sort of portable antenna for my cell phone.

Pete