Lockpicks:

Lockpicks, a tool of the common thief, can also be put to efficient use by the Keepers. Lockpicks allow one to circumvent the use of keys to enter locked doors. This can be very useful in our quest of knowledge. Also, efficient use of lockpicks has often kept our order well-hidden, as no tracks or methods of entry are left.

Note -- it is sometimes necessary to use both lockpicks in a coordinated effort to open advanced or deteriated locks.