Editing Combination lock (section)

===Other designs===
Many doors use combination locks which require the user to enter a numeric sequence on a [[keypad]] to gain entry. These special locks usually require the additional use of electronic circuitry, although purely mechanical keypad locks have been available since 1936.<ref>{{US patent|2029080}}</ref> The chief advantage of this system is that multiple persons can be granted access without having to supply an expensive physical key to each person. Also, in case the key is compromised, "changing" the lock requires only configuring a new key code and informing the users, which will generally be cheaper and quicker than the same process for traditional key locks.

[[electronic lock|Electronic combination locks]], while generally safe from the attacks on their mechanical counterparts, suffer from their own set of flaws. If the arrangement of numbers is fixed, it is easy to determine the lock sequence by viewing several successful accesses. Similarly, the numbers in the combination (but not the actual sequence) may be determined by which keys show signs of recent use. More advanced electronic locks may scramble the numbers' locations randomly to prevent these attacks.

There is a variation of the traditional dial based combination lock wherein the "secret" is encoded in an electronic microcontroller.  These are popular for safe and [[bank vault]] doors where tradition tends towards dial locks rather than keys.  They allow many valid combinations, one per authorized user, so changing one person's access has no effect on other users.  These locks often have auditing features, recording which combination is used at what time for every opening.  Power for the lock may be provided by a battery or by a tiny generator set in operation by spinning the dial.<ref>{{cite web|title=Kaba-MAS X-09 and CDX-09 High Security Locks|url=http://www.kaba-mas.com/pdf/brochures/x_09.pdf|pages=8|date=Dec 2010}}</ref><ref>{{cite web|title=Operating Instruction for the X-09 Type 1F High Security Electronic Lock|url=https://portal.navfac.navy.mil/portal/page/portal/NAVFAC/NAVFAC_WW_PP/NAVFAC_NFESC_PP/LOCKS/PDF_FILES/X-09_Operating_Instructions.pdf|date=December 2010|url-status=dead|archive-url=https://web.archive.org/web/20110728015227/https://portal.navfac.navy.mil/portal/page/portal/NAVFAC/NAVFAC_WW_PP/NAVFAC_NFESC_PP/LOCKS/PDF_FILES/X-09_Operating_Instructions.pdf|archive-date=28 July 2011}}</ref>