Small ID Card GPS Tracker that can warn the wearer when they are too close to somebody else also wearing a device with a gentle vibration reminder, battery operated simply charge up and go then let the powerful online software do the rest for you.
You can remotely configure the device and set up basic parameters — via intuitive portlets. Like the length of time that should elapse before an alert is sent to the server (in seconds), and what the safe distance would be.