Dallas iButton^TM:


Some of the dallas devices can be programmed with extra information to support further features...

There are serveral other devices & technologies that provide a unique ID, and your system then decides what to do based on the ID; eg, other electronic keys, magnetic swipe cards, RFID.

Microchip (among others?) do the technology behind those car cetral locking remote controls.

The advantage of this is that the key itself is uniquely identified.

Using a "secret code" has many problems; eg,

Everyone has to remember the code!

Where more than one person is involved, you need some secure way of communicating the code, and advising changes

How to cope with granting temporary access.

You cannot tell who entered the code - if you suspect that the secret has "leaked", all you can do is change the code. With a unique ID, you just disable the suspect key.

Again, If a unique ID key is lost or stolen, you just disable that key - the only way to tell if a "secret code" has been discovered is after it has been misused!