Inclusion Criteria:  Willing to sign informed consent form Currently taking anti-hypertensive therapy for more than 3 months Drugs are unchanged during the study period Office BP below 140/90 mmHg at least one visit  Exclusion Criteria:  Diagnosed with terminal illness End-stage renal disease requiring lifelong dialysis treatment Patients with impaired performance status (ECOG >= 2) Women undergoing or expecting pregnancy during the study period Resistant hypertension (taking more than 4 kinds of anti-hypertensive drugs) Known atrial or ventricular arrhythmia Wrist circumference out-of range between 13.5 to 21.5 cm