airbag on stairs for safety

How many injuries or deaths do we have every year caused by people falling down stairs? I think stairs should be fitted with sensors to detect feet movement. An airbag should be fitted to the bottom step. If abnormal data is collected by the sensors in steps higher up the stairs, the airbag should be activated to help prevent major injury or death. A combination of weight, pressure and timing could all be combined in to an algorithm to know when to activate the airbag.