The context of this work is the development of a mobility aid for visually impaired persons. We present here an original approach for a real time alerting system, based on the detection of visual salient parts in videos. The particularity of our approach lies in the use of a new feature map constructed from the depth gradient. A distance function is described, which takes into account both stereoscopic camera limitations and user's choices. We also report how we automatically estimate the contribution of conspicuity maps, which enables the unsupervised determination of the final saliency map. We demonstrate here that this additional depth-based feature map allows the system to detect salient regions with good accuracy in most situations, even in the presence of noisy disparity maps.