Patients with chronic obstructive pulmonary diseases (COPD) are usually prescribed supplemental oxygen, especially during outdoor physical activities. However, the GOLD (Global Initiative for Obstructive Lung Disease) guidelines do not provide specific recommendations about oxygen dosage during exercise. Also, previous studies have demonstrated that using resting arterial blood gases to regulate the flow of portable oxygen concentrator does not effectively prevent desaturation during activities of daily living (ADL). On the other hand, some clinicians prefer to individualize oxygen therapy during exercise using several types of stress tests which are mostly inaccurate comparing to the ADL, expensive and time consuming for both physician and patient. Because of the relationship between oxygen desaturation and some activity parameters such as walking velocity and number of steps, we have designed a portable device composed of an Android smartphone to monitor multiple activity parameters, a Pulse Oximeter and a Raspberry pi 3 which communicate with other devices through Bluetooth Low Energy (BLE) in order to find out the relationship between each activity parameter and desaturation during ADL in order to help physicians to prescribe the proper supplementary oxygen therapy. Thanks to the use of Raspberry pi 3 with a powerful quad core microprocessor, other additional sensors equipped with BLE can be connected to the device to synchronously collect the more comprehensive data.