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From Molly (female given name) + guard.

Originally a Plexiglas cover improvised for the Big Red Switch on an IBM 4341 mainframe after a programmer's toddler daughter (named Molly) tripped it twice in one day. Later generalised to covers over stop/reset switches on disk drives and networking equipment.



molly-guard (plural molly-guards)

  1. A physical barrier to protect something from unwanted contact, especially a shield to prevent accidental tripping of an emergency shutdown or power switch.
    There is a plastic molly-guard covering the escalator's shutdown button to prevent little kids from pushing it and stopping the escalator.
    • 1978, Proceedings of the 13th Intersociety Energy Conversion Engineering Conference, volume 3, Society of Automotive Engineers, page 1948:
      The radial heat losses are minimized by the Molly Guard foil which establishes a linear temperature profile between the hot heater housing and the water cooled base plate.
    • 1998 August 10, kensmark, “Vi versus Word. The pros and cons (or why does Vi remiond me of a bigger version of notepad?)”, rec.arts.sf.composition, Usenet,
      Therefore, we have many "molly guards," which are kludged covers that protect the on/off switch and keep you from hitting it by accident.
    • 2008 September 6, Simon Slavin, “Manual on/off switch with electrical off-trip?”, in uk.comp.sys.mac (Usenet):
      To include switch, cut-out and molly guard, you'll probably need to order at least two, probably three components.