Asthma is a chronic air way inflammatory disease that restricts airflow in lungs through acute reduction of airway by a combination of smooth muscle constriction, swelling, and increased mucus secretion. While there is no cure for asthma, the disease can be controlled by avoiding or removing triggers, closely monitoring lung function, and medication management. The home environment is essential to the prevention, control, and treatment of asthma. Home care includes self-monitoring using peak expiratory flow (PEF) device and a written asthma action plan. A peak flow meter is used to measure the volume of forced exhalation, and is a reliable and objective measure to signify potential onset of exacerbation before symptoms are felt, determine the severity of exacerbations, and evaluate treatment. Existing peak flow meters require the user to remember and follow the procedure to take peak flow measurements and thus have reduced compliance. In this paper we propose a low cost, portable, smartphone compatible peak flow meter design that connects to a smartphone through the audio jack.