A breath alcohol testing device has a removable tamper-resistant sampling chamber assembly that provides a disposable interface between the test subject and the alcohol sensor, other sensors and electronics of the testing device. Hydrophobic membranes prevent bodily fluids and other liquids from entering the alcohol sensor and other sensitive components of the testing device. A set of chambers with one-way valves direct the gas flow within the sample chamber assembly to ensure the breath sample delivered to the alcohol sensor is not diluted by the subject inhaling, and is a deep-lung breath sample.