A connector caps that can reduce risk of accidentally removing the cap include a locking feature where outer housing is designed to prevent removal of the cap unless a downward force is applied to the cap with counter clockwise rotation. Structural elements making up the cap locking feature can be optimized or varied, for example to require application of more or less force, more or less downward movement, more or less rotational movement, and variations of other characteristics to facilitate intentional removal and/or to prevent unintentional removal of the cap from the needleless connector, and/or to facilitate securing of the cap on the needleless connector. Optionally, a needleless connector cap can include an outer housing providing holes or openings or vents such that air can pass through if the cap becomes lodged in air passage way.
