Trial of Mobile External Defibrillator for Out-of-hospital Cardiac Arrest in Singapore.

1.1. Inclusion Criteria Study participants must meet all the inclusion criteria to participate in this study: 1. Must be proficient in English. Able to read and understand English fluently. 2. Be aged 21-74 years of age at point of recruitment. 3. Willing and able to move rapidly to a scene that can be 400 meters away from their location. 4. Be a registered CFR with SCDF. 5. Must be active myResponder® mobile phone app user so they can receive alerts about nearby OHCA cases. 1.2. Exclusion Criteria All subjects meeting any of the following exclusion criteria will be excluded from participation in this study. 1. Not proficient in English. Cannot read and understand English. 2. Aged less than 21 and over 74 years of age. 3. Not willing to be a myResponder app user. 4. Not able to move rapidly to a scene that can be 400 meters away from their location. 5. Given the short duration of the trial, those who are pregnant will be ineligible. 6. Those experiencing any serious physical injury or handicap and those with obvious mental handicap.