Indirect airflow measurement through breath-operated device is accomplished by incorporating an airflow sensor into the inhaler device along a low resistance channel disposed away from the exhaust chamber of the device and having an input port in airflow communication with a low resistance channel and output input port and low resistance channel are formed in the main housing body of the device, and further incorporating an output port formed near the exhaust changer near the mouthpiece assembly, the output port also in airflow communication with the low resistance channel. A method of measuring airflow in an inhalation device is also described that measures air flowing through the low resistance channel. Another aspect of the invention provides a method that allows for the closure of the devices' airflow ports, by allowing for the rotation of the mouthpiece assembly from open to closed positions relative to the inhaling device's main housing body and towards handle assembly.