A peak flow meter is a portable, easy-to-use device that measures how well your lungs are working. If you have asthma, your doctor may recommend that you use a peak flow meter to help track your asthma control.In addition to watching for worsening signs and symptoms, such as wheezing or coughing, you can use a peak flow meter to help you decide when you need to act to keep your asthma under control. Regular use of your peak flow meter can give you time to adjust your medication or take other steps before your symptoms get worse. A peak flow meter can be useful for adults and children as young as preschool age.