1. A computer-implemented method for estimating falls risk, comprising: receiving, at one or more processors, first acceleration data from a first inertial sensor attached to a person transitioning from a standing state to a sitting state or from a sitting state to a standing state; receiving, at the one or more processors, second acceleration data from a second inertial sensor attached to the person; receiving, at the one or more processors, falls history information of the person; determining, from the first acceleration data, a first value indicating timing of the person's transitioning between the sitting state and the standing state; determining, from the second acceleration data, a second value indicating steadiness of movement of the person; generating, at the one or more processors, a classifier model based on the first value, the second value, and the falls history information of the person.