no creativity, nobody tried anything

No. Nobody dies from lifting their feet. They die from stepping outside. So half my suggestions are still on the table.

A buzz sound? Who gives a crap? I'm talking about life and death, and you're talking about a buzzer?

Here's what we know, the one thing that kills them is in front of them. If the person in front of you dies, why not use them as a human shield? The thing would shoot the dead body. Doesn't matter who you touch or where you stand if it blocks the shot.

You offhand dismiss every idea without a shred of substantiation. I didn't start the thread so someone could just say "no". I watched the movie, I don't need you to re-write it so my ideas are answered. They weren't. You just saying it would be pointless is utterly irrelevant.

And no, If aliens invaded I wouldn't stand around or get dinner. I'D LEAVE OR FIGHT. Standing around is the stupidest thing to do.

And no, there's nothing at all to indicate the people at the end of the film survived the space ship. They are just some random people standing around. I can see cars driving around in the background, people walking around. No indication the city was empty at all. What we do see is people in a back neighborhood standing around.

Though remember the pregnant woman? The stomach lay onto another circle and nothing happened.

Thank you. The one person realizing this is about making a fictional film more interesting.

Your assessment is not accurate. Regardless of how the movie played off up until that point, the very last scene practically obliterated the abstraction you're referring to, grounding the movie into a much more mundane premise by way of showing us exactly what was all really about thus leaving very little room to speculation. From the very moment you're grounding your story like that, trains of thought based on those grounds, like the OP's, are justifiably set in motion.

Also, that other thread the creators of the movie opened where they're giving specific answers to concrete questions isn't helping the defense for the abstract thought experiment case neither, with every new bit of info they're giving grounding the thing even more in run-of-the-mill science fiction fare and every new explanation opening two more gaps on the whole thing's internal logic for each one it attempts to close. Just the very fact that such an advanced alien civilization would set up this humongous plan as a population control scheme theoretically based on the target species' behavior and criteria under stress as a basis for the fairest and more impartial-ish triage process they're able to come up with may sound, in narrative fiction terms, all fine and dandy... if the rules of the selection process were clearly stated and understood by each subject beyond any shadow of doubt, even before the ordeal even starts. As it is, the very first individuals killed by the "process" while the target group members are barely just coming to their senses and trying to get a grip of what the hell's going on around them may've very well been the more fit or worthy of surviving the circle, actually. For a process theoretically devised to put the weight of the responsibility for the triage criteria into the collective hands of the target subjects there's too much room left for error, pure luck and plain randomness to decide the final outcome. Even statistically and mathematically speaking, the conclusion that the percentage of "worthy" -as in, selflessness tagged as such by their kin- individuals left amongst the planet's population after the purge would be higher than if it were instead the plain result of a random Columbine-like shootout happening simultaneously at a worldwide level would be a naive notion at best. I could picture that if the objective of the whole thing was some kind of data recollection process set up by a very advanced civilization obsessed by morals and the study of intelligent alien species' behavior, but that notion was shoot down by the creators of the movie themselves by plainly comparing the invaders' actual motivations to the kind of animal population control criteria and measures so often applied by our own human species regarding others that are collectively perceived as "lesser". Albeit it's also plainly stated that the aliens' process was designed, as mentioned before, as a way of putting the weight of the decision of who gets to survive on the target populations' collective shoulders... which would be fine and dandy if such criteria -or, at the very least, the process' strict rules- were CLEARLY set beforehand as to ensure the fairest outcome possible under such dire circumstances. As it is, the only reasons why it isn't so are strictly for storytelling conventions, meant to create suspense and woven a serviceable narrative. Which would be OK if it didn't conflict with the ultimate logic by which the whole concept's driven. It's a no-no-win situation overall.

As always, please excuse my English if I misused some expression; I'm not a native speaker and I'm not even formally trained so I try to do my best whenever I need to explain my way around any complex subject that calls for a fair amount of reasoning. Thanks.

Also, a few more thoughts and a bit of a reflexion. Despite any side "thought experiment" and allegorical considerations and from a purely narrative standpoint, if the story you're writing has to rely heavily on a given gimmick you need to concentrate a big chunk of your efforts unto foolproofing that gimmick beyond expectations. Both the triage rules and the actual mechanical behavior of the device setup proves to be too serviceably arbitrary plotwise during the story's development -specially the final "twist" with the pregnant girls' belly falling conveniently over the vertical axis of a life sensor without the system caring at all- as to not question its looseness and exploitable fails from an internal logic point of view and to not concede the OP some credit for arguing about the obvious flaws of the way such a central element has been laid off in the film. His questions and arguments are perfectly valid and don't come from a failing to understand the film's plot or development but spawn from those same plot and development's obvious faults, whether you're more or less prone to overlook those faults, partial or totally. They're there anyway.