Perception of breath is a simple but unfailing tool for increasing mental alertness. As stated, the technique lays down that one should be fully aware of each and every inhalation as well as exhalation. Obviously this is possible only if the mind is alert and wakeful.
Otherwise the respiration will be mechanical and not conscious. Regular practice of conscious breathing and its perception increases the alertness of mind and there will be total awareness and concentration. Thus, it is a simple positive technique for awakening the mind and keeping it alert.
Once the mind has been fully awakened, its restlessness and wanderings vanish and it is trained to concentrate on the matter in hand.