The Singapore Red Cross Society recently updated its Rapid Rescue iPhone app that'll help visitors and residents in distress. The app lists all 12,000 first-aiders in Singapore and lets you put out a call for help. When an SOS is requested, an alert goes out to all first-aiders within a 2 KM radius. One of these workers can accept the request and get a map to the person in distress.
If there are no first-aiders nearby, users can call for an ambulance or follow the provided route to the nearest hospital, instead. New first-aiders can also use the app to add themselves to the database. The app is available for free from the iOS App Store and is only compatible with Singapore Red Cross providers.