The flawed basic premise

1) The creatures have bulletproof armour. The mother kills one at the end because they frequency of the hearing-aid disrupts the creature's ability to keep its armour up.
2) Gunfire or noise would just attract even more creatures to the area
3) Regarding military response, we have to assume that the reason the creatures took over is because they reproduce extremely quickly, not just because they are bulletproof, fast and strong.

I've read creator John Krasinski's comments on the backstory for this film. It goes something like this:

A decent sized asteroid impacts in Mexico. It destroys everything for hundreds of miles in every direction. That asteroid turns out to be a fragment of a distant extrasolar planet that was torn apart, perhaps by a black hole or collision with a rogue planet. These creatures were intelligent but pretechnological apex predators on their homeworld. Their armor is resilient enough to have protected them from the explosion of their planet, the journey through space, re-entry, and a high velocity impact. So yeah - it's incredibly tough. We don't know if they reproduce quickly or there were simply a lot of eggs delivered by that asteroid which were scattered about during atmospheric entry and then hatched.

Whatever the case, they overran the Earth very quickly. Cities became all-you-can-eat buffets for the creatures. Something like a MOAB - or of course a nuke - might kill them at very close range but small arms, .50 caliber rounds, even grenades and missiles, are useless. As Krasinski put it, until they expose themselves they're practically invulnerable. We've seen how fast they are when they move quickly. You can imagine hundreds or thousands of those things being drawn to the sound of the guns, tearing soldiers apart, ripping open tanks like tin cans (remember how the claws on one of them sliced right through that thick steel silo door?).

As we saw when people turned on their lights in a nightly show of solidarity, more survivors are out there than it appears at first. The smart and resourceful ones who came up with a system of doing what they need to do silently have survived. Probably 95% of the world's population, or more, are gone though. Government and military leaders may still be around, taking refuge in underground facilities like Cheyenne Mountain, but they're not going to be much help to the people outside.

There are definitely questionable elements to the story though. It seems a little silly that they had to walk around barefoot all the time - sneakers aren't any noisier. And when human beings first determined these creatures used sonar to see, you'd think someone would've thought of high intensity sound as a way to "blind" or even incapacitate them. Just as animals like dogs with extremely sensitive hearing are vulnerable to high volume, high frequency sound. I would have expected the army to try that. Also when they open their mouths to eat you, how about firing your gun down their throat? That ought to work. And they do unfold some of their armor plates to expose the hearing organs while hunting. A sniper should be able to take them out from a safe distance.

Groups of people, both civilian and military, would develop tactics of diversionary noisemaking to cover the shooter's gunshot (on top of their using a silencer). As they got better they'd feel comfortable enough to move from defensive killings to going on the hunt themselves. Of course the aliens, being intelligent, communicate with each other and would be trying to figure out what you were doing. In other words you'd have to vary your tactics. They wouldn't keep falling for the same simple trap over and over again, and might even turn the tables if you weren't careful. Clever girl!

Another thing hinted at by John Krasinski was that the father was studying the aliens' vocalizations with his equipment, trying to learn their language. That could make for some interesting plot developments going forward. They've already got a sequel planned. It seems likely mother and daughter can handle the two creatures coming for them. But what will they do then? Abandon their home and go looking for other people? They can't be the only ones who have figured out how to kill the aliens. Maybe folks in other places have established an uneasy truce of sorts by killing enough of the creatures that they won't come too close to town anymore. Or the magnetic field they generate (which interferes with electronics) could be used by simple detectors to trigger ultrasonic shriekers that would drive them away. Set up a perimeter and as long as you had electricity they couldn't get past it.

Yeah. Everyone in this world would be coming up with concepts based around sound making devices

* Bring some noise making toys with you at all times. In case you happen to make a noise that draws the monsters to you, just throw one of these toys as a "sound grenade" to divert the monster's attention.

* Place remote triggered sound devices everywhere in the area around your home, for the same purpose.

* Attract monsters to certain areas to attempt to destroy them, or just to study them. Use a drone, a kite with a speaker or whatever.
Being able to stand around silently and control a noise-making device would be very easy. And everyone would wanna study these monsters in order to figure out how they work, and what their weaknesses might be.

We see the adults use an alarm clock and rockets to draw them off. At no point, did it not occur to them: "Hey, let's use noise to draw these things into a barn / bottom of a well / lake and then kill them with guns / arrows / gasoline / electricity!"