Passive alcohol tests measure alcohol in the air, which may come from an open beer can or the exhaled breath of an intoxicated person. When using a passive alcohol test device the subject is asked to blow at, or to speak towards the passive test device. The passive alcohol test device detects any alcohol in the breath. Passive devices cannot accurately measure intoxication levels; their role is as a pass/fail test to identify individuals who have been drinking.

Examples of passive alcohol test devices include the P.A.S. IV flashlight alcohol detector, the P.A.S. Sentry, and the P.A.S. Vr.  The Alco-Sensor FSTcan be operated either as a conventional direct breath tester or as a passive test device.

One advantage of passive alcohol test devices is they do not use mouthpieces, eliminating a significant operating cost.  Devices like the Alco-Sensor FST use sampling cups to help funnel the subject’s breath into the device.  However, because subjects do not touch their mouth to the sampling cup, there is no need to change the sampling cup after every test.