Objective: This investigation aimed to assess the feasibility and accuracy of the CART-I Plus, a novel ring-type cuffless blood pressure (BP) measuring device and compare its performance with standard 24-hour ambulatory BP monitoring (ABPM). Design and method: The study recruited 40 patients, of which 33 were included in the final analysis. Participants were instructed to wear both the CART-I Plus and the ABPM devices on the same arm for a duration of approximately 24 hours. The BP readings obtained from the CART-I Plus, which utilizes photoplethysmography (PPG) signals for measurement, were compared against those from the ABPM. Results: In terms of systolic/diastolic blood pressure (SBP/DBP) readings, the CART-I Plus recorded values of 131.4±14.1 / 81.1±12.0 mmHg, 132.7±13.9 / 81.9±11.9 mmHg, and 128.7±14.6 / 79.3±12.2 mmHg for the 24-hour, daytime, and nighttime periods, respectively. In comparison, the ABPM showed readings of 129.7±11.7 / 84.4±11.2 mmHg, 131.9±11.6 / 86.3±11.1 mmHg, and 124.5±13.6 / 80.0±12.2 mmHg for the same intervals. The mean variances in SBP/DBP between the CART-I Plus and ABPM were 1.74±6.69 / -3.24±6.51 mmHg, 0.75±7.44 / -4.41±7.42 mmHg, and 4.15±6.15 / -0.67±5.23 mmHg for the 24-hour, daytime, and nighttime measurements, respectively. Furthermore, a significant correlation was observed between the devices, with correlation coefficients of r=0.725 for SBP and r=0.750 for DBP during the transition from daytime to nighttime (both p <0.001). Conclusions: The CART-I Plus device, with its innovative ring-type design, demonstrates considerable accuracy in BP measurement, aligning closely with the established ABPM method. These findings indicate that the CART-I Plus could be an effective tool for continuous BP monitoring in clinical settings. Its ability to provide consistent and reliable measurements, along with the convenience of its cuffless design, highlights its potential as a valuable addition to current BP monitoring practices.