Safes. They are big, heavy, and make us feel, well, "safe" about our valuables stored inside.
Historically, safes were controlled by a series of complex gears that only the correct series, or "combination", of dials would open. I loved the illustrations for gears and other mechanical devices in David Macaulay's "New Way Things Work".
Digital safes, whether the professional variety of the home variety, were created largely for convenience. They are faster to open, easier to share (and change) codes, and required less physical space for all of the gears.