Breathe in, and then turn the key. This is the process that DUI offenders in many states need to repeat every time they want to start their car. An ignition interlock device (IID) or a breath alcohol ignition interlock device is a breathalyzer installed on the motor vehicle's dashboard. These little cell-phone sized devices work as lock to keep you from starting your engine. The driver must exhale into the breathalyzer and their analyzed BAC must read at less than the set BAC limit on the device. This is usually 0.02% to 0.04% but it varies from state to state. If your BAC is over the limit, your car will not start.

Sometimes, even if you start the car successfully, an ignition interlock device will require another breath sample. This is because some drivers will have a friend take the breath test for them, and then hop behind the wheel intoxicated. If the driver is intoxicated, then the system will record the offense, and set off an alarm or some other annoyance until the driver pulls over and turns off the engine. The interlock device will not shut off the engine immediately in this situation, since that could create dangerous collisions, but the honking and alarms should be enough to get the offender off the road.

The updated ignition interlock devices use what is called an "ethanol-specific fuel cell" as a sensor to detect the driver's BAC. This is not as accurate as the infrared spectroscopy technology that is used in official breathalyzers, but it is cheaper to manufacture. In-car breathalyzers not only test the blood alcohol content, but they record every test done. This data is calibrated every month or two, and police can read the log to detect violations. These devices cost about $150 to install and an additional $75 a month. If you are required by law to install one, you will have to foot the bill.

Since 2009, almost all 50 states allow a judge to impose the ignition interlock device on a repeated DUI offender. In Arizona, all DUI offenders are mandated six months with an IID, regardless of whether or not the charge was for alcohol. Californians who are driving on a suspended license are required to drive with an IID for up to three years from the date of their conviction. In four counties (Alameda, Sacramento, Tulare, and Los Angeles) all DUI convicts must install an IID in order to receive restricted driving privileges. In Georgia, offenders with a second DUI must install an IID in their car for six months.

Massachusetts and North Carolina also have varying laws requiring drivers charged with a second DUI to put this machine into their car. In Utah, anyone convicted of a DUI is required to install an IID. New Mexico only requires an IID for first time offenders, while the state of New York requires any person driving while intoxicated to install an IID on every vehicle that they own and operate.

Currently, Mothers Against Drunk Driving, known as MADD, is campaigning for these breathalyzer tests. They want legislation to demand that all convicted drink drivers install these locks in their cars. According to the Community Guide, these devices, when mandated, reduce DUI re-arrests by 67 percent. The IIDs are well made- they are programmed with anti-circumvention techniques so it is impossible to use a phony breath sample. If the driver tries to leave his or her car running when at the bar, and then drive away afterwards, that won't work either. The test will randomly ask for breath samples while the car is running, and if no sample is given, this will be recorded as a violation on the log. Disconnecting the IID battery won't eliminate that log, it will stored on a back-up file accessible to police. There are a few glitches in the system: drivers who are taking medicines or using mouthwashes with an alcohol base may not be able to get their car to start for work. If you have been issued an IID, plan accordingly. If you were falsely accused with a DUI, then you will want to contact a DUI attorney and discuss your situation.