Background. Previous studies have examined the application and benefits of sensors, both in sports and health. Unfortunately, the design of sensor-based isometric contraction examination tools after ankle sprain injuries and ankle instability is still rarely carried out. Purpose. The aim of this research is to design a sensor-based isometric contraction examination tool after ankle sprain injury and ankle instability. Material and Methods. The design used is research and development involving experts, namely instrumentation physics, sports physiology, and physiotherapy to assess the suitability of the tool before field trials. The tool developed is the “Isometric Contractions Test”, which is designed in the form of a box with dimensions of 10 cm (height) x 10 cm (width) x 25 cm (length). Various electronic components are also used, such as Arduino Pro Mini, Flexi Sensors, switch buttons, and OLED LCD as digital reading output. A total of 10 participants aged 18-23 years participated voluntarily for the field trial. Participants were men and women who had experienced sub-acute or chronic ankle sprains and ankle instability. The data obtained were analyzed using the correlation method. Result. The results of this study report that this sensor-based isometric contraction examination tool is valid, reliable, effective, and practical in detecting and treating post-injury healing of ankle sprains and ankle instability. Conclusions. This tool can be used to assist physiotherapists in carrying out observations and evaluations to treat healing quickly and precisely, both in athletes and non-athletes.