The patent basically involves three main components: a detector for sensing when the shoe wears out; a processor to measure the detector's data; and an alarm for alerting the user when a shoe is no longer stable. Sensors can be of any type, including accelerometers, pressure sensors and piezoelectric flexing sensors, among others. Data is processed through an algorithm, which can be set according to a shoe manufacturer's specifications, that determines at what point a shoe is at the threshold of failure.