战备警巡 combines 战备, combat readiness or war preparedness, with 警巡, patrol-and-alert operations. In official PLA usage, the phrase marks an operation as a readiness posture rather than ordinary patrolling or training. It signals that the force is acting in response to a real or asserted security condition.
That distinction matters at Scarborough Shoal. Southern Theater Command did not describe the June activity as 巡逻, routine patrols, or 演习, exercises. It used language tied to territorial defense and operational readiness. The term does not prove the scale or frequency of the activity, but it does reveal the category Beijing chose for it.