Many system makers have standardized on barcodes and chips, with chips catching on with users often seeking out a system with a diversity of applications.
Made by Maxim/Dallas Semiconductor of Dallas, Texas, the iButton is a computer chip with a unique 64bit address encased in a 16mm stainless steel “can.” The stainless steel “can” does double duty: to protect the chip inside and for its electronic communications interface. Each “can” has a data contact which is called the “lid” and a ground contact which is called the “base.” By simply touching each of the two contacts you can communicate to any iButton and read its address in less than 5 milliseconds. The basic 64bit iButton is in most guard tour systems.