Hi Loopey
Best thing to me sounds like you need an app to run on an Android or (scummy, massively overrated) iPhone.
I've checked the Android Market and there are plenty of apps available for what you want. 'EmergencyAlert' is a free app that claims 'If you meet emergency situation, you touch this widget two times and your phone automatically calls a registered number with alarm and vibration'.
There is another app (costs £1.50ish), called iSOS Emergency Alert that, with a single touch, triggers emergency calls, text messages, emails (and Facebook and Twitter updates!) to 5 of your chosen contacts. It can automatically call 911 (I guess 999 too!) and tells them your GPS-position so people can find and help you easily.
That second one sounds exactly what you need really. You'll need an Android phone for that one I suspect. But no-one else will so there'll only be a cost for one of them (and they're free with many mobile contracts).
There are plenty of apps by the look of it that will be useful for what you want.
Dan