The lifetime risk for development of atrial fibrillation, the commonest sustained arrhythmia in adults, is estimated to be 24%-27% for individuals of 40 years or older. Previous work showed that annual new diagnosis of AF is 11000-26000 in Hong Kong. Other arrhythmia such as supraventricular arrhythmia or premature beats were also common and of clinical significance. 12-lead ECG is a first line investigation for patients with suspected paroxysmal arrhythmia, but it has a low diagnostic yield with its 10-30 seconds recordings. 24-hour Holter exam is the usual next step of diagnosis. The diagnostic yield of Holter varies according to indication but is generally low at 1%-12%. This is because paroxysmal arrhythmia may not happen every day. In addition, even if arrhythmia is picked up in Holter, patient may not register the symptom, making the symptom arrhythmia correlation problematic. Despite limitations, the demand for Holter exam is still high. In Prince of Wales Hospital, a tertiary referral centre with a catchment of about 1 million populations, the waiting time for a routine Holter exam is 3 years. Smartwatch has gained popularity over past years as an adjunct to smartphone. Latest generations of smartwatch were equipped with wearer-initiated ECG rhythm strip recording capabilities. Smartwatch has evolved to become a health tracker with arrhythmia detection capabilities. It was found to be a useful tool for atrial fibrillation screening in general population. Other arrhythmias, such as supraventricular tachycardia, premature beats, and abnormal ECG patterns associated with sudden cardiac death could also be detected with smartwatch ECG recordings. Apple Heart study was the largest study utilizing smartwatch for arrhythmia detection. The general population was screened for atrial fibrillation using irregular pulse algorithm. The study found a 84% concordance rate between irregular pulse notification and ECG patches. Therefore, investigators propose to conduct a study to compare its diagnostic yield with Holter, in patients with suspected arrhythmia and see if smartwatch recording following a systematic protocol for four-weeks will have better arrhythmia diagnosis yield than a 24-hour Holter exam.