This is a circuit composed of electronic components, which have the following function: will capture ambient sounds through an electret microphone, and play in a small speaker, will also have a volume control, and when sounds above 85 db for example are played (shooting a firearm) circuit and cut the sound will not play.
Some features: preferably use electronic components easy to find (common components) or have to use a microcontroller that is the PIC family.
We also have to have a low consumption. circuit power let the discretion of the developer.
I would like the circuit had few components to be as small as possible.