Bare alpha track detectors are sensitive to radon progeny as well as to radon gas. This paper reports the test results for two brands of bare alpha track detectors that received several radon exposures at three progeny concentrations. The results show a relationship that is a linear combination of both the radon gas and the radon progeny concentrations. The reported radon concentration depended on the equilibrium factor assumed by the processor. The sensitivity of bare alpha track detectors increases with altitude, but this is a minor, correctable effect compared to the equilibrium factor.