 Chronic Obstructive Pulmonary Disease COPD is a common, long term condition of the lungs that is usually caused by cigarette smoking. In addition to daily symptoms and limitation in activities, patients are prone to developing chest infections called exacerbations. Exacerbations are a big problem: unpleasant for patients, and sometimes severe enough to cause hospital admission and therefore health facilities pressures and death. Reducing the impact of exacerbations is very important. We have previously shown that earlier treatment of COPD exacerbations results in faster recovery, and reduced chance of hospital admission. Helping patients to detect exacerbations early is therefore important. We have also recently shown that monitoring heart rate and oxygen saturation via a finger probe may assist in this. However, measuring these variables when the patient is awake means they can be affected by other things, such as exercise and anxiety. Our new idea is that measuring heart rate and oxygen level overnight, when a patient is asleep, will give the best chance of detecting COPD exacerbations early and our study will test that. We will randomly allocate 64 patients with COPD recruited from our service in London to standard monitoring, or overnight monitoring, for up to six months or the first exacerbation, whichever is sooner. We will then analyse whether overnight monitoring was able to detect exacerbations earlier, and therefore could be used to help patients get treatment earlier. A subset of participants will also wear an activity monitor overnight for the first two weeks, so that we can assess the effect if any of overnight awake periods such as trips to the bathroom on the heart rate and saturation recording. 