Jarek,

Take a look at

           http://patent.womplex.ibm.com/

and see patents (among about 100 others) 5,300,922 - 5,574,431 - 4,413,254
- 4,622,542 - 3,983,552 - 4,074,249 - 3,820,104 - 4,063,229 - 4,993,245 -
5,572,191 - 5,008,649 - 3,895,368 - 5,510,770 - 5,300,922.......

and I think you'll know everything about how the whole security-tag stuff
works....

Albert Smulders
InSAD - Encarnaci—n, Paraguay
insad@itacom.com.py