A circuit protection device comprising: a substrate comprising a first electrode, and a second electrode; a sliding contact positioned on the substrate at a first location, wherein at the first location the sliding contact is connected to, and provides a conductive path between, the first electrode, and the second electrode, via a sensing element; a spring element configured to move the sliding contact to a second location upon loss of resilience of the sensing element, wherein at the second location the sliding contact does not provide a conductive path between the first electrode, and the second electrode, wherein the sensing element is configured to lose resilience upon detection of any one of the following activation conditions: an over current condition; and an over temperature condition; characterised in that: (i) the circuit protection device is a three-function circuit protection device; (ii) the substrate further comprises a heater element, the heater element being configured to receive an activation control current; (iii) at the first location the sliding contact is connected to and provides a conductive path between, the first electrode, the second electrode and the heater element via the sensing element; (iv) at the second location the sliding contact does not provide a conductive path between any of the first electrode, the second electrode, and the heater element; and (v) the sensing element is also configured to lose resilience upon detection of an activation condition of an activation control current received by the heater element. a substrate comprising a first electrode, and a second electrode; a sliding contact positioned on the substrate at a first location, wherein at the first location the sliding contact is connected to, and provides a conductive path between, the first electrode, and the second electrode, via a sensing element; a spring element configured to move the sliding contact to a second location upon loss of resilience of the sensing element, wherein at the second location the sliding contact does not provide a conductive path between the first electrode, and the second electrode, wherein the sensing element is configured to lose resilience upon detection of any one of the following activation conditions: an over current condition; and an over temperature condition; an over current condition; and an over temperature condition; characterised in that: (i) the circuit protection device is a three-function circuit protection device; (ii) the substrate further comprises a heater element, the heater element being configured to receive an activation control current; (iii) at the first location the sliding contact is connected to and provides a conductive path between, the first electrode, the second electrode and the heater element via the sensing element; (iv) at the second location the sliding contact does not provide a conductive path between any of the first electrode, the second electrode, and the heater element; and (v) the sensing element is also configured to lose resilience upon detection of an activation condition of an activation control current received by the heater element. (i) the circuit protection device is a three-function circuit protection device; (ii) the substrate further comprises a heater element, the heater element being configured to receive an activation control current; (iii) at the first location the sliding contact is connected to and provides a conductive path between, the first electrode, the second electrode and the heater element via the sensing element; (iv) at the second location the sliding contact does not provide a conductive path between any of the first electrode, the second electrode, and the heater element; and (v) the sensing element is also configured to lose resilience upon detection of an activation condition of an activation control current received by the heater element.