A sensor (300, 600), comprising: a first electrically conductive element (310, 610) and a second electrically conductive element (360, 660); an electrically insulative element (340, 640) connected to the first electrically conductive element and the second electrically conductive element, where at least a portion of the first electrically conductive element and at least a portion of the second electrically conductive element make contact with the electrically insulative element; and at least one electrically conductive piece (390, 690) located within a cavity of the sensor, wherein the conductive piece has a diameter, and the cavity is defined by at least one surface of the first electrically conductive element, at least one surface of the first electrically insulative element, and at least one surface of the second electrically conductive element; wherein a diameter of a distal portion of the first electrically conductive element and a diameter of a distal portion of the second electrically conductive element are smaller than a diameter of the electrically insulative element; the first electrically conductive element (310, 610) having a first diameter on a proximate portion of the first electrically conductive element (310, 610) and a second diameter on a distal portion of the first electrically conductive element (310, 610), where the second diameter of the first electrically conductive element is smaller than the first diameter of the first electrically conductive element (310, 610); and the second electrically conductive element (360, 660) having a first diameter on a proximate portion of the second electrically conductive element (360, 660) and a second diameter on a distal portion of the second electrically conductive element (360, 660), where the second diameter of the second electrically conductive element (360, 660) is smaller than the first diameter of the second electrically conductive element (360, 660), and wherein the distal portion of the first electrically conductive element (310, 610) faces the distal portion of the second electrically conductive element (360, 660); characterised in that the at least one electrically conductive piece (390, 690) is an electrically conductive spring, and in that the at least one electrically conductive spring (390, 690) is fixed to an inner surface of the second electrically conductive element and is moveable inside the cavity between: a closed position, when the sensor is at rest, wherein there is electrical conduction provided between an inner surface of the first electrically conductive element and the inner surface of the second electrically conductive element, and an open position, wherein there is no electrical conduction provided between the inner surface of the first electrically conductive element and the inner surface of the second electrically conductive element. a first electrically conductive element (310, 610) and a second electrically conductive element (360, 660); an electrically insulative element (340, 640) connected to the first electrically conductive element and the second electrically conductive element, where at least a portion of the first electrically conductive element and at least a portion of the second electrically conductive element make contact with the electrically insulative element; and at least one electrically conductive piece (390, 690) located within a cavity of the sensor, wherein the conductive piece has a diameter, and the cavity is defined by at least one surface of the first electrically conductive element, at least one surface of the first electrically insulative element, and at least one surface of the second electrically conductive element; wherein a diameter of a distal portion of the first electrically conductive element and a diameter of a distal portion of the second electrically conductive element are smaller than a diameter of the electrically insulative element; the first electrically conductive element (310, 610) having a first diameter on a proximate portion of the first electrically conductive element (310, 610) and a second diameter on a distal portion of the first electrically conductive element (310, 610), where the second diameter of the first electrically conductive element is smaller than the first diameter of the first electrically conductive element (310, 610); and the second electrically conductive element (360, 660) having a first diameter on a proximate portion of the second electrically conductive element (360, 660) and a second diameter on a distal portion of the second electrically conductive element (360, 660), where the second diameter of the second electrically conductive element (360, 660) is smaller than the first diameter of the second electrically conductive element (360, 660), and wherein the distal portion of the first electrically conductive element (310, 610) faces the distal portion of the second electrically conductive element (360, 660); characterised in that the at least one electrically conductive piece (390, 690) is an electrically conductive spring, and in that the at least one electrically conductive spring (390, 690) is fixed to an inner surface of the second electrically conductive element and is moveable inside the cavity between: a closed position, when the sensor is at rest, wherein there is electrical conduction provided between an inner surface of the first electrically conductive element and the inner surface of the second electrically conductive element, and an open position, wherein there is no electrical conduction provided between the inner surface of the first electrically conductive element and the inner surface of the second electrically conductive element.