Carbon dots (CDs) are a type of fluorescent nanomaterial that have gained significant attention due to their simple synthesis method and excellent optical properties. The unique structure of CDs also allows for effective luminescence tunability. CDs have been reported to be pH-sensitive in many studies. However, most of these reports are based on the variation of the luminescence intensity of CDs with pH change. There are few reports on exploring the linearly tunable variation of the luminescence wavelength with pH value. Hence, we synthesized novel pH-sensitive CDs using a simple solvothermal method. The synthesized CDs can change their luminescence emission wavelength by simply adjusting the pH of the solution. The change in emission wavelength may be due to the alteration in the surface state of the CDs caused by the pH change. This luminous color change of the CDs allows for visual detection of the pH of the solution. In addition, a color-changing hydrogel composite for pH sensing was designed based on the pH sensitivity of the CDs. The CDs@hydrogel has conductive properties that enable it to be used for motion sensing and sweat pH detection.