| CPC G08B 21/18 (2013.01) [G08B 5/36 (2013.01)] | 16 Claims |

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1. Apparatus comprising a flexible substrate applied to a surface of the apparatus, the flexible substrate comprising:
at least one visual indicator element;
at least one detector configured to detect access to the apparatus consistent with a cleaning operation; and
processing circuitry configured to control a visual indication state of the at least one visual indicator element in response to a detection by the at least one detector of access to the surface of the apparatus; and
conductive tracks that connect the processing circuitry to the at least one visual indicator element and the at least one detector;
wherein the at least one detector is configured to detect an instance consistent with a cleaning operation of the surface being required;
wherein the at least one detector is disposed at the surface;
wherein the at least one detector comprises:
a heater element and a gas detector element, wherein the heater element is configured to heat a local area of the surface, and the gas detector element is configured to detect the instance consistent with the cleaning operation being required in response to detecting emission of one or more gases from the local area heated by the heater element indicative of the presence of contaminants;
wherein the at least one visual indicator element, at least one detector, processing circuitry, and conductive tracks have been printed onto the flexible substrate.
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