Raghav was returning with his family from a marriage party. On the way, a traffic policeman stopped their car. He asked Raghav’s father who was driving the car to exhale his breath into an instrument to check whether he has drunk or not. After checking from the instrument, he allowed them to go. As a student of chemistry: Can you explain the theory behind this test ?

Raghav was returning with his family from a marriage party. On the way, a traffic policeman stopped their car. He asked Raghav’s father who was driving the car to exhale his breath into an instrument to check whether he has drunk or not. After checking from the instrument, he allowed them to go. As a student of chemistry: Name the instrument used by the traffic policeman.