Crack growth damage is a common threat for the conservation of a wide range of museum heritage such as statues, plasters, fresco paintings, faience and wooden artefacts that are exposed to mechanical, thermal or hygroscopic swelling stresses. Optical Fiber Bragg Grating (FBG) sensors offer a sub-miniature solution for crack and temperature monitoring that is minimally-invasive, hardly visible and sensitive enough to track even the micro-evolution of the crack growth. Furthermore, FBG sensors do not interact with radio-frequency and microwave fields and can be employed for real-time temperature monitoring during microwave killing of xylophages. In this work we developed an improved FBG sensor installation technique that is completely removable and sensitive also to crack opening reduction. In this paper the theoretical foundations, the design of the sensor application the step-by-step installation instructions and some real applications to marble and bronze statues and to paintings on wood are described.