A fire suppression system comprising: a mechanical fire detection line, wherein the mechanical fire detection line includes a tensioned line (110; 208, 210) and one or more sensors that are linked together via the tensioned line (110; 208, 210); and a tension indicating device (200; 300), the tension indicating device (200; 300) comprising: a body comprising a first end and a second end, at least one of the first and second ends configured to be operatively coupled to the tensioned line (110; 208, 210) of the mechanical fire detection line; and a piston configured to be slidably disposed along a length of the body, the piston comprising a piston head and a connecting rod, wherein a free end of the connecting rod extends towards the at least one of the first and second ends, wherein the free end is configured to be coupled to the tensioned line (110; 208, 210) of the mechanical fire detection line, and wherein the piston head is provided with a movable indicator, wherein responsive to the tensioned line being provided with tension, the piston moves towards the at least one of the first and second ends of the body, thereby causing the movable indicator to correspondingly move along the length of the body of the tension indicating device (200; 300) to indicate a tension in the tensioned line of the fire suppression system, and wherein the tension indicating device further comprises a reference indicator provided on the body of the tension indicating device (200; 300), wherein the reference indicator is located, such that when the movable indicator is in alignment with the reference indicator, the tension indicating device (200; 300) indicates that the tensioned line (110; 208, 210) is correctly tensioned, wherein a correct value of tension is a range of tension values that allow the one or more sensors to be held intact in the absence of fire and allow a suitable change in tension to be experienced on breakage of any of the one or more sensors in order to provide a control signal. a mechanical fire detection line, wherein the mechanical fire detection line includes a tensioned line (110; 208, 210) and one or more sensors that are linked together via the tensioned line (110; 208, 210); and a tension indicating device (200; 300), the tension indicating device (200; 300) comprising: a body comprising a first end and a second end, at least one of the first and second ends configured to be operatively coupled to the tensioned line (110; 208, 210) of the mechanical fire detection line; and a piston configured to be slidably disposed along a length of the body, the piston comprising a piston head and a connecting rod, wherein a free end of the connecting rod extends towards the at least one of the first and second ends, wherein the free end is configured to be coupled to the tensioned line (110; 208, 210) of the mechanical fire detection line, and wherein the piston head is provided with a movable indicator, wherein responsive to the tensioned line being provided with tension, the piston moves towards the at least one of the first and second ends of the body, thereby causing the movable indicator to correspondingly move along the length of the body of the tension indicating device (200; 300) to indicate a tension in the tensioned line of the fire suppression system, and wherein the tension indicating device further comprises a reference indicator provided on the body of the tension indicating device (200; 300), wherein the reference indicator is located, such that when the movable indicator is in alignment with the reference indicator, the tension indicating device (200; 300) indicates that the tensioned line (110; 208, 210) is correctly tensioned, wherein a correct value of tension is a range of tension values that allow the one or more sensors to be held intact in the absence of fire and allow a suitable change in tension to be experienced on breakage of any of the one or more sensors in order to provide a control signal. a body comprising a first end and a second end, at least one of the first and second ends configured to be operatively coupled to the tensioned line (110; 208, 210) of the mechanical fire detection line; and a piston configured to be slidably disposed along a length of the body, the piston comprising a piston head and a connecting rod, wherein a free end of the connecting rod extends towards the at least one of the first and second ends, wherein the free end is configured to be coupled to the tensioned line (110; 208, 210) of the mechanical fire detection line, and wherein the piston head is provided with a movable indicator, wherein responsive to the tensioned line being provided with tension, the piston moves towards the at least one of the first and second ends of the body, thereby causing the movable indicator to correspondingly move along the length of the body of the tension indicating device (200; 300) to indicate a tension in the tensioned line of the fire suppression system, and wherein the tension indicating device further comprises a reference indicator provided on the body of the tension indicating device (200; 300), wherein the reference indicator is located, such that when the movable indicator is in alignment with the reference indicator, the tension indicating device (200; 300) indicates that the tensioned line (110; 208, 210) is correctly tensioned, wherein a correct value of tension is a range of tension values that allow the one or more sensors to be held intact in the absence of fire and allow a suitable change in tension to be experienced on breakage of any of the one or more sensors in order to provide a control signal.