How do Ignition Interlock Devices Work?

Maybe you have heard about the new bill that proposes mandatory IIDs for first time DUI and DWI offenders in Maryland. Or perhaps you have just heard the term IID mentioned recently and are curious as to what one is, or perhaps you have been convicted with a DUI and are now required to drive with an ignition interlock device installed on your vehicle.

Either way, you may have some questions about IIDs. In this post, we hope to answer your questions and to show you why working with a DUI attorney in Maryland is your best course of action after being arrested for driving under the influence.


An ignition interlock device, or IID, is a small device intended to prevent drunk driving. An IID is connected to a vehicle’s ignition system and will prevent the engine from starting if the driver fails a breath BAC test.

How Does an IID Work?

An IID is similar to a Breathalyzer used to measure blood alcohol concentration levels during DUI arrests. It requires the driver of the vehicle to perform a breath BAC test before allowing the vehicle’s engine to start.

Most IIDs work using fuel cell technology, but there are still some on the market that use semi-conductors. Semi-conductor IIDs tend to be less accurate and can produce “false positives.” False positives record the driver as having a BAC that is higher than the pre-determined limit, even if the driver is completely sober.


An ignition interlock device also requires drivers to perform “rolling tests.” These tests require the driver to pull over and perform another BAC test in order to continue to be allowed to drive. These are performed to ensure that drivers do not start their car sober, and then drink while they are driving. If you do not perform the rolling test after a period of time, the car’s engine will automatically shut off.

In addition to preventing you from starting your car, an IID records information on your test results and driving habits. According to the MVA’s website, ignition interlock devices are required to record the following information:

  • You (the driver), your vehicle, and other program information;
  • Any instances where you had a high blood alcohol concentration (BAC);
  • Any instances where you tried to start the vehicle without taking the test;
  • Any instances where you failed the rolling retest or refused to take it;
  • Any bypass of the device, which is if you tampered with or disconnected the device;
  • The number of times your vehicle was started and stopped;
  • The distance traveled by your vehicle.

Who is Required to Have an Ignition Interlock Device?

In addition to having your license suspended after being convicted of driving under the influence of alcohol, you may also be required to have an ignition interlock device installed in your vehicle.

In the state of Maryland, repeat offenders convicted of driving under the influence are required to have an ignition interlock device installed on every car that is registered to the defendant. A person is considered a repeat offender in Maryland if they are convicted of more than one DUI in a five year period. Repeat offenders are required to keep the IID on their cars for at the minimum of one year.

However, first time offenders can also be required to have ignition interlock devices depending on the circumstances and sentencing of their DUI case. For instance, if a first time offender’s BAC was exceedingly high, a Maryland judge may require him to install an IID on his vehicle.

Some people voluntarily install ignition interlock devices on their vehicles. They may choose to do so for several reasons. For example, a parent might install an IID to ensure that his newly licensed teen does not drink and drive or a business owner might require IIDs to be installed on all company vehicles.

How Much Does an IID Cost?

Most ignition interlock device manufacturers like to soften the blow of the cost of their products by claiming that they cost less than a large cup of coffee per a day. But if you do the math, the actual cost of installing and maintaining an IID can anywhere from $550 to well over a $2,000 a year.

Here is break down of the costs associated with an ignition interlock device in the state of Maryland:

  • Installation: at least $100 (per vehicle)
  • Monthly Maintenance: $60-80 (per vehicle)
  • Monthly Rental Fee: $50-100 (per vehicle)
  • Restricted License Fee: $20
  • Removal of Restricted License Fee: $20

Mandatory participation in Maryland’s Ignition Interlocking Program can also be time consuming. You must schedule monthly appointments to recalibrate the device and retrieve the recorded information. If you fail to register enough “starts” or register too many “failed starts” then you must schedule an appointment with an IID servicer within 5 days. Also, some IIDs can perform what is called a “permanent lockout.” This means that you must have the vehicle towed to a state approved IID servicer, costing you even more time and money.

Want to Avoid the Costs of an IID?

The best way is to not drink and drive. Having an IID installed in your vehicle is just one of the many costs of a DUI.

However, people do make mistakes, and an arrest for driving under the influence is not an automatic conviction.


If you are facing subsequent DUI charges, or have been arrested for your first offense, now is the time to call a reputable DUI attorney in Maryland. If you want to avoid the cost and hassle of installing and maintaining an ignition interlock device on all of your registered vehicles, hire Dilip Paliath, an experienced DUI attorney in Maryland.

Dilip Paliath, Esq.

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