Generally, in the 23rd century, this precaution was unusual at a spacedock, when starships were on the ready inside. A flaw of yellow alert status in this time was that minor warnings in the ship data banks didn't process a likely red alert event, such as a faulty module which lives depended on for safe beaming. Also, starships were prone to overloads when key crewmembers were unavailable to man posts. (TOS movies: The Motion Picture, The Search for Spock)
In the 24th century, sensors automatically raised shields and prepared computers for whatever outside stimuli dictated. One design flaw also corrected was the minimization of shipboard communications and readings that warrant unwanted scanning. Warp engines and impulse thrusters also had their power signatures masked by background subspace static or natural space phenomena. Certain actions cannot bypass yellow alert, such as using a tractor beam, de-pressurizing a deck, or traveling within the gravity field of a planet. Performing or receiving sensor sweeps usually illicited this as well. (TOS episode: "Balance of Terror", TNG episode: "When the Bough Breaks", Star Trek: Starfleet Academy (game) (SNES))
Aboard the USS Enterprise-D, the yellow alert led to all bridge stations becoming fully active and enabled, with diagnostics of the tactical and primary systems. Also, the operations manager would limit activities that could be a hindrance to emergency preparedness. (TNG video game: Echoes from the Past)
Yellow alert was more often done "manually", by vocal command; from a foreseeable dilemma. "Automatic" came into play when a physical disturbance occured near/to the ship's hull.
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