This is a fantastic idea! A recent news story on the BBC highlighted the release of smart bracelets for aid workers.
The new bracelets allow civil rights and aid workers to trigger an alarm when at risk, e.g. of being kidnapped or killed. When activated, the bracelet uses phone and sat-nav technology to send messages to Facebook and Twitter. Messages include details of the wearer and their location when the alarm was activated.
Great idea ,I like to know more . is it available in GERMANY ?