Abstract: A calibration checking device, and methods of mandating its use at regular time intervals, to ensure maintenance of the accuracy of gas analyzers, especially for use with breath tests. Each calibration checking device is designed to be used for a predetermined number of tests. After first connection of a new calibration checking device, a volume of known calibration checking gas is released into the instrument, and a calibration checking measurement is initiated. A signal is sent to a counting mechanism which both enables the use of the instrument, and commences a count of the number of tests performed by the breath tester. When the number of tests is exceeded, the instrument is disenabled. The device can include a moisture filter having an interface with the instrument, which prevents its operation if the filter is used beyond the recommended number of times, or if excess moisture renders it saturated.