It would depend on the volume it's within.
Alcohol will distribute or diffuse into the space where there's no.... It goes from an area of high concentration to an area of low concentration. It diffuses very rapidly. The larger the area for diffusion, the greater the chance of the alcohol falling below a detectable level, for any device.
I seriously doubt that anyone would want to have a device that could be used two feet away from someone. There's just far too much that can happen in that two feet.