Deconstruction of Voice Overs in Film Noir

Within the Film Noir genre it is common to have a first person voice over. The main character is usually the voice over. It allows the audience to get a clear picture of what is happening in the film and shows the story from the detectives/villains/protagonists point of view. As well as this a voice over can give extra details in addition to what the audience can see on the screen. An example of this is in 'Double Indemnity':

  NEFF
                              (His voice is now 
                              quiet and contained)
                          It began last May. About the end of 
                         May, it was. I had to run out to 
                         Glendale to deliver a policy on some 
                         dairy trucks. On the way back I 
                         remembered this auto renewal on Los 
                         Feliz. So I decided to run over there. 
                         It was one of those Calif. Spanish 
                         houses everyone was nuts about 10 or 
                         15 years ago. This one must have 
                         cost somebody about 30,000 bucks -- 
                         that is, if he ever finished paying 
                         for it.

By having the voice over from the detectives point of view, as seen above, the audience can get to know this specific character in detail therefore evoking certain emotions such as sympathy or fear for this particular character. 

The voice over may include details of the characters back story to describe what they are about to do in the film and why they are doing it. It may also include what the character is thinking and feeling about certain situations or other characters within the film. 

Normally the voice over is male however in our opening scene we may subvert this convention and use the female, femme fatale, as the voice over as this would make more sense with our storyline.