Alcocat's breathalyzer is not waterproof. Keep it in a dry place. Gently clean the breathalyzer with a damp fabric if needed.

To maintain accuracy, we recommend you calibrate the device every year or after 300 readings using a certified BAC (Blood Alcohol Content) liquid wet bath solution. Use only certified BAC mixtures between 0.01% to 0.05% blood alcohol at any breathalyzer calibration service provider. See calibration guide here

If you haven't used the breathalyzer in more than 24 hours, you should take a second measurement after a couple of minutes. Micro-dust particles in the air cover the sensor and give lower BAC results for the first measurement.
What else? Just treat your Alcocat breathalyzer same way you treat your smartphone.