The investigators designed a device that makes an acoustic record each time an inhaler is used. Opening the device makes an acoustic file which is recorded, this file is "time-stamped" which means that the timing of drug administration is recorded. When the device is retrieved and acoustic analysis performed, the steps involved in using the inhaler can be determined. Hence, the subjects inhaler technique is assessed and errors in the inhaler use identified. Together this means that errors in inhaler technique and timing of use can be quantified.