Inspired by this question SF short story, maybe titled "House by the side of the road", about a human at a remote interstellar site guarding against alien invasion I have one on a similar theme. I read it in the UK in the 1980s, an unremembered SF anthology.
A man on a remote asteroid emerges from a bungalow inside a brightly lit atmosphere force field at the same time every day. He potters about in a sunlamp garden for an hour or two and then sits on a verandah. Day after day for many months.
One day a spacecraft lands and two aliens come out and begin talking as they near his force field. He stands and stares as they approach.
His translation machine gives him something like... "We have been observing you for many days, what is your purpose in being here on this remote rock?"
He turns without speaking and presses a switch, instantly the aliens are held trapped in restraint force fields. At the same time a signal is sent back to Earth.
Day after day the aliens plead and beg with him (I think they were described as cute looking white teddy bears) as they grow weaker with hunger and finally die.
He waits patiently for his rocket home, knowing his mission is accomplished, mankind will now be able to learn all about yet another galactic race to conquer and exploit, like they've done to all the others.
Edit: This story is NOT Panic Button by Eric Frank Russell.