She advised his parents to use a special device called a peak flow meter.

VOA: special.2009.07.28

Depending on his or her age, your child may use a hand-held device to measure how well he or she can breathe (peak flow meter).

CNN: Childhood asthma

In a few minutes Lorelei brought out the peak flow meter, and when Davis blew into it he was back nearly to his normal reading of 380.

NPR: In 'Challenger Park,' Mom Is an Astronaut