How do you instruct an aircraft to turn on their automatic altitude transponder?

The phrase "Squawk altitude" is the standard phraseology used in air traffic control to instruct pilots to activate their altitude reporting on the transponder. This terminology is concise and widely understood among pilots and air traffic controllers. The word "squawk" refers to the setting of a specific code on the aircraft's transponder that communicates with radar systems, and adding "altitude" indicates that the aircraft should also report its altitude.

While the other choices may convey a similar intention, they are not in accordance with standard aviation phraseology. For example, "Activate altitude squawk" and "Turn on the altitude transponder" are more verbose and do not adhere to the established brevity and clarity that are vital in aviation communications. "Please report your altitude" is a request for the pilot to verbally provide their altitude instead of using the transponder, which would not achieve the same effect of automatic altitude reporting. Thus, using the correct phrase "Squawk altitude" facilitates effective communication and ensures that air traffic controllers receive timely altitude information from the aircraft.