Beacon – Send an alert when stopped
As it says on the tin. Maybe integrate with device accelerometers/sensors to detect a crash, or at the least send a notification to the Beacon contacts if the activity has paused, perhaps with a user configurable time interval before sending an alert. Brownie points for integrating with the Strava app on the recipient end. Providing location info and alerts through the app for the person riding/running/whatever without needing to refresh a browser.