A tamper-evident fastening device for use with a wristband, wherein the device comprises: a casing comprising two separate portions; and a divider which is adapted to retain two portions (5a, 5b) of a strap of the wristband, wherein the two separate portions are positioned on each planar surface of the divider such that two substantially parallel paths of the strap are defined between the divider and the casing, wherein each path is defined between the casing and one planar face of the divider, and wherein the divider and the casing are configured such that they are capable of being connected together via an irreversible lock, wherein the divider comprises a first and second retaining member (4, 2), wherein the first retaining member is arranged to hold a first end portion of a strap so that longitudinal movement of the first end portion is inhibited, wherein the divider further comprises at least one resiliently biased engagement member, and the casing further comprises at least one housing arranged to engage the engagement member of the divider and prevent the casing from opening once closed, wherein the first retaining member depends from and extends substantially perpendicular to the divider and is arranged to extend through the first end portion of the strap, and wherein the second retaining member is arranged to extend through the second end portion of the strap, characterised in that the second retaining member is arranged to hold a second end portion of the strap such that movement of the second end portion in a first longitudinal direction is enabled and movement in a second, opposite longitudinal direction is inhibited, and the second retaining member is arranged to intersect the second end portion of the strap at an acute angle. a casing comprising two separate portions; and a divider which is adapted to retain two portions (5a, 5b) of a strap of the wristband, wherein the two separate portions are positioned on each planar surface of the divider such that two substantially parallel paths of the strap are defined between the divider and the casing, wherein each path is defined between the casing and one planar face of the divider, and wherein the divider and the casing are configured such that they are capable of being connected together via an irreversible lock, wherein the divider comprises a first and second retaining member (4, 2), wherein the first retaining member is arranged to hold a first end portion of a strap so that longitudinal movement of the first end portion is inhibited, wherein the divider further comprises at least one resiliently biased engagement member, and the casing further comprises at least one housing arranged to engage the engagement member of the divider and prevent the casing from opening once closed, wherein the first retaining member depends from and extends substantially perpendicular to the divider and is arranged to extend through the first end portion of the strap, and wherein the second retaining member is arranged to extend through the second end portion of the strap, characterised in that the second retaining member is arranged to hold a second end portion of the strap such that movement of the second end portion in a first longitudinal direction is enabled and movement in a second, opposite longitudinal direction is inhibited, and the second retaining member is arranged to intersect the second end portion of the strap at an acute angle.