In all likelihood to signal for this demonstration of his planet's power.

5 seconds sound clip from the The Day the Earth Stood Still (1954) classic radio play.

You can hear this line at 00:37:02 in the radio play.

Quote context

[...]

- I wish I could be more specific, but all communications are out.

- I can tell you that we are preparing to declare a state of national emergency, but before we start discussing plans, I want a report from Colonel Ryder.

- All I can report, General, is that the robot at the spaceship was discovered to have moved last night.

- It knocked unconscious the two soldiers guarding the entrance to the shed the Army Engineers had built around the spaceship...

- Indicating that someone, presumably the space man, had wanted to get into the ship for one reason or another.

- In all likelihood to signal for this demonstration of his planet's power.

- Go on, Colonel.

- Well, that's all, sir.

- Now, gentleman... Until now we've agreed on the desirability of capturing this 'man' alive.

- We can no longer afford to be soft in this matter. We will get him alive if possible, but we must get him!

- Is that clear, gentlemen? Dead or alive. Get him.

[...]