The major difference between home blood-alcohol machines and the devices used by law enforcement is that those used by police are certified and tested for accuracy.
"For a Breathalyzer test result to be admissible in court, we have to show the machine has been inspected and property calibrated on a regular basis by a licensed examiner," Champaign County State's Attorney Julia Rietz said.
The testers sold to U.S. consumers are certified by the Food and Drug Administration. Those used by law enforcement must be approved by the Department of Transportation's National Highway Traffic Safety Administration.
Nancy Easum, supervisor of the Alcohol and Substance Section for the state police, said more than 900 alcohol testing instruments used to provide evidence for court cases in Illinois must be checked at least every 62 days.
Easum said state statutes give the state police discretion to set the number of days.
She said 62 days provides enough time for the technicians to go out into the field and check all the machines, but also is a short enough time to prevent long-running errors.
Dave Henebry is one of 10 technicians who check the machines to make sure they are accurate within 10 percent of .082 of a gram per 210 liters of breath.
While home devices generally cost no more than $150, Easum said the machines used in police cars cost about $2,600. Larger stationary machines cost about $5,800.
"Virtually all of our breath testing instruments work by taking whatever alcohol is in a person's breath and letting a fuel cell make electricity out of the alcohol in the breath," Henebry said.
Henebry said the instruments need to be checked for specific locations because the readings can vary based on barometric pressure and elevation above sea level.
Before testing someone, officers first get a blank reading to make sure there is no leftover substance in the machine from a previous user, Rantoul police Officer Eric Ruff said.
Ruff said he will have the person being tested wait at least 20 to 25 minutes after eating, smoking or drinking before the test begins in order to get an accurate reading. Then the machine requires a person to breathe into a tube for about six seconds.
Rantoul Police Chief Paul Farber said that if a person tries to blow out of the side of his mouth to try to beat the machine, the device will note it has received insufficient air to test. After three such incidents, Ruff said, it is the same as refusing to take a test, and the driver's license may be suspended.
This story appeared in print on Feb. 5.