A population of locatable personal detection units (PDUs) (20) are worn by users. Any number of locators (14) are placed at known locations within an area (10) where the users tend to be. When an alarm event for an individual user occurs, a request signal is transmitted from the user's PDU (20). The...http://www.google.com.au/patents/US5661492?utm_source=gb-gplus-sharePatent US5661492 - Personal alarm location system and method
