In one embodiment, an apparatus comprises a mount, a housing, and a sensor. The mount is adapted to be disposed at least partially underneath a shoelace of a shoe. The housing is configured and arranged to be placed in at least first and second states in relation to the mount, wherein in the first state the housing is movable with respect to the mount and in the second state the housing is immovable with respect to the mount. There is a tongue on one of the mount and the housing and a groove on the other of the mount and the housing, the tongue being adapted to engage the groove when the housing is in the second state in relation to the mount and to disengage the groove then the housing is in the first state with respect to the mount. The sensor, which senses motion of the shoe, is disposed within the housing such that the sensor remains disposed within the housing when the housing is placed in the first state in relation to the mount and the housing is moved with respect to the mount.