Possible Clues:

• Item on a superintendent's chain
• The master doing the business in the opening movement
• Fitter in many locks
• All-purpose door unlocker
• Device that can open different locks
• Minimum personnel on shift for instance that can provide maximum access
• Bob maybe having vital 'Access all areas' pass?
• It can open a lot of doors for you
• Kent lose terribly important opening all-rounder?
• Item on a Halloween ring?