A digital breathalyser will need regular re-calibration to make sure that it is retaining its accuracy. For the models with a semi-conductor sensor this usually means simply purchasing a new breathalyser sensor about every 6 months, and fitting it yourself. Some of the newer fuel cell sensor models also have a sensor which you can change easily yourself. Models such as the Draeger 6820 breathalyser
will require returning to a calibration centre.