Open door notice

Hello everyone,
I have a Peugeot 206 and when I am circulating with it and it takes a small bump usually jumps a warning that the left rear door is open, and it is not true, since I have checked it and is always closed.
I would like someone to advise me that it can be and how to solve that breakdown.
Thank you all and say that I love this page has helped me in many moments with my car, but now this breakdown has come out.
Thanks again to everyone

Czech the switch that is at the door itself, it could be that it is making bad contact or that that the cable itself is in poor condition, nothing records or another world.