The system uses just ROM address of iButton, that mean you can use any iButton as a key even temperature probes and such. Now this bring another thought about security. First I consider iButton secure, but they can be read and copied, so can be RFID tags. Also touching probe with iButton is more convenient than to type 16 hex digit on keypad. But it can be surely improved. For example if you stay with iButton there is NVRAM version like DS1992. It gives you 1Kb of non volatile RAM you can use for floating code that can be generated every time you touch authorization unit. This makes coping much more complicated.
iButton for its price and durability. Maxim states "Thanks to sealed stainless steel, you can drop it, step on it, or scratch it. The iButton is wear-tested for 10-year durability and a million hot contacts."