A wheel speed sensor comprising: an electromagnetic sensor (52; 202), comprising: a substantially box-shaped electromagnetic sensor head (60; 206) disposed at a distal end of the electromagnetic sensor (52; 202), the electromagnetic sensor head (60; 206) comprising a magnet and an integrated circuit, the electromagnetic sensor head (60; 206) being configured to sense movement by a tone ring comprising magnetic attractive material; a communication connector (54; 204) disposed at a proximal end of the electromagnetic sensor (52; 204) and in communication with the electromagnetic sensor head (60; 206); a sensor interface disposed at the distal end of the electromagnetic sensor (52; 202), the sensor interface comprising a slot extending about at least three sides of the substantially box-shaped electromagnetic sensor head (60; 206), wherein the slot is defined by a narrow lip at a front end of the electromagnetic sensor head (60; 206), and a separate retainer element; and a flange having an annular shape and comprising a spacer for receiving a wheel shaft of a vehicle through an open bore aperture of the flange, the flange including a flange interface comprising a pair of parallel spaced arms projecting outwardly from the flange with respect to an axis of the bore aperture, each of the spaced arms including a projection at an outward distal end thereof, wherein the projections of the arms face towards each other; wherein the electromagnetic sensor (52; 204) is configured such that it can be secured to the flange interface by insertion of the substantially box-shaped electromagnetic sensor head between the pair of spaced arms of the flange interface, wherein a lip at a rear of the sensor head (60; 206) contacts the arms while the slot is adjacent an opposing side of the arms, and by securement of the retainer element within the slot of the substantially box-shaped electromagnetic sensor head (60; 206). an electromagnetic sensor (52; 202), comprising: a substantially box-shaped electromagnetic sensor head (60; 206) disposed at a distal end of the electromagnetic sensor (52; 202), the electromagnetic sensor head (60; 206) comprising a magnet and an integrated circuit, the electromagnetic sensor head (60; 206) being configured to sense movement by a tone ring comprising magnetic attractive material; a communication connector (54; 204) disposed at a proximal end of the electromagnetic sensor (52; 204) and in communication with the electromagnetic sensor head (60; 206); a sensor interface disposed at the distal end of the electromagnetic sensor (52; 202), the sensor interface comprising a slot extending about at least three sides of the substantially box-shaped electromagnetic sensor head (60; 206), wherein the slot is defined by a narrow lip at a front end of the electromagnetic sensor head (60; 206), and a separate retainer element; a substantially box-shaped electromagnetic sensor head (60; 206) disposed at a distal end of the electromagnetic sensor (52; 202), the electromagnetic sensor head (60; 206) comprising a magnet and an integrated circuit, the electromagnetic sensor head (60; 206) being configured to sense movement by a tone ring comprising magnetic attractive material; a communication connector (54; 204) disposed at a proximal end of the electromagnetic sensor (52; 204) and in communication with the electromagnetic sensor head (60; 206); a sensor interface disposed at the distal end of the electromagnetic sensor (52; 202), the sensor interface comprising a slot extending about at least three sides of the substantially box-shaped electromagnetic sensor head (60; 206), wherein the slot is defined by a narrow lip at a front end of the electromagnetic sensor head (60; 206), and a separate retainer element; and a flange having an annular shape and comprising a spacer for receiving a wheel shaft of a vehicle through an open bore aperture of the flange, the flange including a flange interface comprising a pair of parallel spaced arms projecting outwardly from the flange with respect to an axis of the bore aperture, each of the spaced arms including a projection at an outward distal end thereof, wherein the projections of the arms face towards each other; wherein the electromagnetic sensor (52; 204) is configured such that it can be secured to the flange interface by insertion of the substantially box-shaped electromagnetic sensor head between the pair of spaced arms of the flange interface, wherein a lip at a rear of the sensor head (60; 206) contacts the arms while the slot is adjacent an opposing side of the arms, and by securement of the retainer element within the slot of the substantially box-shaped electromagnetic sensor head (60; 206).