A proximity alert was an alert signal aboard a starship that indicated when another vessel was approaching.

In 2373, Lieutenant Tom Paris was alerted of an approaching Kazon ship vessel by the computer in his shuttlecraft. (VOY: "Basics, Part II")

In 2374, Seven of Nine's sensory nodes were being affected by the Mutara-class nebula. She hallucinated that the computer verbally stated that Trajis Lo-Tarik's vessel was approaching the USS Voyager. (VOY: "One")