A Holter monitor is a small, wearable device that records a continuous ECG, usually for 24 to 48 hours. Wires from electrodes on your chest go to a battery-operated recording device carried in your pocket or worn on a belt or shoulder strap. While you're wearing the monitor, you'll be able to go about your normal activities, as long as you keep the electrodes and device dry. In addition, your doctor will likely ask you to keep a diary of what you're doing when symptoms occur and the time. Your doctor will compare the diary with the electrical recordings to try to figure out the cause of your symptoms.