A composition, and methods of making and using such a composition, whereby the composition can include a printable ink formulation having a colorant which undergoes a visible color change upon exposure to a wetness threshold. The colorant can be highly resistant to leaching. Additionally, the colorant can be resistant to premature activation via ambient moisture or humidity.

A composition, and methods of making and using such a composition, whereby the composition can include a printable ink formulation having a colorant which undergoes a visible color change upon exposure to a wetness threshold. The colorant can be highly resistant to leaching. Additionally, the colorant can be resistant to premature activation via ambient moisture or humidity.

There is described a sensing device for attaching to an external surface of a nappy. The sensing device comprises an expandable member comprising one or more elastic elements extending between a plurality of attachment points, wherein the attachment points are configured to fixedly attach the expandable member to the external surface of the nappy, and wherein the one or more elastic elements are configured to stretch as the attachment points move apart such that the expandable member is configured to expand in accordance with expansion of the nappy. The sensing device further comprises a detector unit coupled to the expandable member, wherein the detector unit is configured to detect expansion of the expandable member, and is further configured to determine a nappy fullness parameter based on the detected expansion of the expandable member.