Existing monitoring methods for lateral friction resistance in open caisson construction have inherent limitations, such as high requirements and difficulties. Consequently, a novel direct test device for lateral friction resistance is independently designed and developed. The finite element software is used to analyze the strain and maximum stress at the beam end under various sensor parallel beam sizes and the strain loss of the device under different sealing fillers. This analysis guides the selection of sensor size and sealing fillers. Additionally, a large direct shear apparatus is employed to calibrate the device accurately. Subsequently, the proposed device was applied in a caisson project in Harbin, China. This research produces the following results: (1) Decreasing the thickness and increasing the length of the parallel beam results in greater microstrain of the elastic element under load, although the maximum stress concurrently increases. (2) Introducing a sealing material into the sensor leads to a particular strain loss, with 10% sealing strain loss observed for the device with a silicone structure. (3) Calibration curves under different normal stresses exhibit good consistency, with linear fitting coefficients exceeding 0.99, indicating device stability. Field application results reveal that the distribution patterns of lateral friction resistance and lateral earth pressure obtained from the lateral friction resistance monitoring device are closely aligned. The device is easy to install, and its results are reliable.