Originally Posted by
WillCAD
I don't know how this passive sensor works, but I imagine that if you only open your window by a fraction of an inch, just enough to let in sound, the passive breath sensor won't be able to get a decent sample of your breath.
A lot of these things are concealed in the flashlights cops use during evening traffic stops or at DUI checkpoints. That's why it's important to not roll down your window far enough to let the cop shove the flashlight into your car in front of your face.