In A Quiet Place, there was a device like an earbud in the ear of the daughter, Regan, on day 472. Later, her father gives her a new device which she refused at first, but later wore it on her head and ear. To test it, she made a sound with her fingers but apparently she didn't hear anything. I would like to know why - because in a scene, when the alien is near her in farms, there's a sound which irritates her ear and tris to cover her ear, maybe to stop that irritation (and in the end too), so makes me think it works or not.
Towards the end, we discover that it creates some sound which irritates the creatures.
In the last scene, she picks up a few items from the table and her mother touches her head to explain something, which I didn't get. (What were those items?)
So what was the purpose of those devices? And what's difference between those two devices, the one she wore before and she wore later?
PS: If possible, kindly don't explain me the ending of movie. I've seen it but I don't want to know what exactly happened (or would happen) in the end of movie.