Prior to a macroscopic landslide displacement, the sliding force drives soil particles near the slip surface to rearrange and alter the soil porosity. This phenomenon may microscopically release infrasonic signals in advance, which can be used for monitoring landslide-prone areas. In this paper, an infrasonic-based device has been designed for monitoring landslides. Slope model tests in the laboratory were performed to investigate the relationship between infrasound and the sliding force. The results show that the dominant frequencies of the infrasonic signal from inner soil masses range from 1.00 to 4.10 Hz. A qualitative correlation between the macro-sliding force and infrasonic signal has also been established. The sliding force is essential for the occurrence of a landslide and its correlation with the corresponding infrasound will be useful in monitoring landslides.