Original Publication Date: 1981-Jan-01
Included in the Prior Art Database: 2005-Feb-10
Access to secure areas can be controlled by badge readers which only open a door if an authorized badge is inserted. However, once the door is opened, any number of people can enter the secure area without inserting their own badge into the badge reader. To insure that each person entering the secure area inserts his badge, three sonic sensors, triangularly positioned, as shown in Fig. 1, are used.