Abstract: According to the present invention there is provided a device that may be worn by a person, or fitted to an apparatus for monitoring, sensing or controlling one or more parameters such as, but by no means limited to, moisture, temperature, heart rate or respiration rate, or controlling various parameters of electronic functions.

Abstract: An identifier comprising at least two machine readable components (62, 64) wherein at least one of the components (64) is capable of being changed from an original value to a modified value in response to a stimulus. In particular it provides for identifiers having codes such as bar codes or pictographic codes, with part of the codes being formed from a material which changes colour in response to a stimulus such as heat, atmosphere or flow of an electric current such that the value of the code as read by a machine may be changed to indicate that the identifier has been exposed to the stimulus. Also disclosed in an identifier formed by applying a light coloured material over a dark coloured surface such that gaps in the light coloured material form a machine readable code.