There are various methods for detecting loose bolts, including: the sound detection method, which determines whether a bolt is loose by listening to the sound produced when the bolt becomes loose. This is a non-contact detection method and is typically used for quick inspections of equipment. The piezoelectric sensing technology utilizes the piezoelectric effect of the medium material. When the bolt becomes loose, there will be a pressure change, which can be captured by a piezoelectric sensor and converted into an electrical signal to achieve the detection of bolt looseness. The optical fiber sensing technology can install the optical fiber sensor near the bolt. By monitoring the tiny movement or deformation of the bolt, it can detect the looseness. This technology has the advantages of high sensitivity and resistance to electromagnetic interference. The ultrasonic attenuation method uses the attenuation characteristic of ultrasonic waves when propagating in the medium to detect the looseness of the bolt. When the bolt becomes loose, the attenuation of the ultrasonic waves will change, which can be detected. Each method has its applicable scenarios and advantages and disadvantages. When applying in practice, it is necessary to select the appropriate detection method based on the specific equipment and environmental conditions. In industrial applications, multiple detection methods are usually combined to improve the accuracy and reliability of the detection.