I will show you how to implement a Sound sensor with an Arduino, LED and Buzzer which can be helpful in home automation, alarm system etc.
The ideal here is just to take a reading (usually a knock on the door or just pick sound of certain frequency) from a sensor. Then flash and sound a buzzer or alarm for notifications.

The materials I used were readily available the Store. Below are the materials I used with their links in the store and they are very few:

Arduino Mega (you can use any other Arduino for yours)
Passive Buzzer
Sound Sensor
Arduino IDE

I have included the full code and connection diagrams in the full post