Processing alert signals from positioning devices

An apparatus, wherein the apparatus comprises or cooperates with a positioning server system configured to track a respective location estimate for each of several positioning devices and to maintain descriptive information on each of several users, each of whom is associated with a respective positioning device;

• wherein the apparatus further comprises:
• a memory system for storing program instructions;
• a processing system for executing the program instructions;
• a database system for storing the respective location estimates for the set of positioning devices;
• and
• an alert signal reception system for receiving at least one alert message from one or more alerting positioning devices, wherein each alert message conveys identifying information of the alerting positioning device that sent the at least one alert message;
• wherein the apparatus is configured to:
• use the identifying information conveyed in the at least one alert message to retrieve from the database system the location estimate for the one or more alerting positioning device;
• and
• determine a first set of other positioning devices in a vicinity of the at least one alerting positioning device and to send an assist request message to each of the positioning devices in the first set of other positioning devices.

A method comprising the following acts performed by a data processing apparatus, which comprises or cooperates with a positioning server system configured to manage a database storing respective location estimates for each of several mobile positioning devices and to maintain descriptive information on each of several users, each of whom is associated with a respective mobile positioning device:

• receiving one or more alert messages from an alerting mobile positioning device, wherein each alert message conveys identifying information of the alerting mobile positioning device that sent the one or more alert messages;
• using the identifying information conveyed in the one or more alert messages to retrieve from the database a location estimate of the alerting mobile positioning device;
• determining a first set of other mobile positioning devices in a vicinity of the alerting mobile positioning device;
• and
• sending an assist request message to each of the mobile positioning devices in the first set of other mobile positioning devices.