I want to make a door knock sensor which will analyze the knock pattern, and I have SW-420 and KY-002 sensor modules. I want to know what is the difference between those two and which one should I use. Thanks.
Do post links to the specific sensors. Compare the data sheets of the sensors and you'll find the differences. Whether those are important to you, depends on your project.
Show us you've done your homework and you'll get much more response!