Texas DWI Bond Conditions: Interlock, SCRAM and Monitoring

Bond conditions are the part of a DWI case people live with every day, long before anything is decided.

A device in the car. A bracelet on the ankle. A weekly test. Rules about where you can be at night. All of it imposed while you are still presumed innocent, and all of it running for as long as the case takes, which can be a year.

Two things are worth knowing. Some of these conditions are required by statute and some are entirely discretionary, which means some of them can be argued about. And the devices can be wrong, in ways that are documented and specific, which matters enormously if one of them flags you.

What a bond condition has to be

A magistrate may impose any reasonable condition of bond related to the safety of a victim of the alleged offense or to the safety of the community. That is the general grant of authority under Texas Code of Criminal Procedure article 17.40, and it is broad.

It is not unlimited. A pretrial bond condition has to satisfy three standards at once. It must be reasonable. It must serve to secure the defendant’s attendance at trial. And it must relate to the safety of the alleged victim or of the community.

That three-part test is the most useful thing on this page, because it is what makes a condition arguable. If the conditions on your release are not the problem so much as the amount, that is a different argument and it is covered in how bail gets set. A condition that does nothing to get you to court, and nothing for anyone’s safety, does not become valid just because a magistrate wrote it down.

Note that conditions on bail pending appeal run under a different and looser framework, where in some circumstances the only requirement is that the condition be reasonable. Texas courts have upheld conditions after conviction that would be harder to justify before it, including a prohibition on driving at all, precisely because the pretrial three-part test no longer applies. If you are reading this after a conviction rather than before trial, the rules being applied to you are different.

When is an interlock required?

Installation of an ignition interlock device is required by Texas Code of Criminal Procedure article 17.441, and the trigger is not the same for every charge. For driving while intoxicated, flying while intoxicated, and boating while intoxicated, it applies only where the charge is a subsequent offense. For intoxication assault and intoxication manslaughter, and since 2019 for DWI with a child passenger, it applies on a first charge.

Four details decide whether it applies to you:

It applies to all bond types. This is not limited to personal bonds. Cash and surety bonds carry it too.

On a DWI, the charge has to allege a subsequent offense. The statutory language appears to require that at the time of release the charging complaint alleges the DWI to be a subsequent offense. If the paperwork does not, that is worth raising. This does not help on a child passenger, intoxication assault, or intoxication manslaughter charge, where no prior is needed.

On a DWI, only priors within the preceding five years count. A conviction outside that window does not trigger the requirement.

The deadline is 30 days. The magistrate must require installation before the 30th day after release.

The scope of the restriction is broader than people expect. The device goes on the vehicle you own or the one you most regularly drive, and you may not operate any motor vehicle unless it is equipped with a device.

That last point deserves emphasis because it differs from the post-conviction rule. The bond version requires the device for all driving by the accused, and unlike the post-conviction interlock, there is no exception for a vehicle owned by your employer. People who know about the employer exception from the occupational license context assume it applies here. It does not.

Installation is at your expense, and the agency responsible for verifying it may charge a monthly monitoring fee capped at $10.

How to be excused from the interlock

There is a real exception and it is underused.

A magistrate may not require installation of the device if the magistrate finds that requiring it would not be in the best interest of justice. The court holds a hearing and then decides whether the device is appropriate in the particular case.

That is a live request, not a formality. The kinds of justifications that carry weight are practical rather than sympathetic:

• Loss of a job, where you are employed by someone else and the device would cost you the position
• Negative impact with co-workers, clients, or customers who would see the device

The common thread is that the device would do harm out of proportion to what it accomplishes, in a case where nothing about your situation suggests you will not appear or that anyone is at risk. That framing tracks the three-part test.

If the device is going to be a genuine problem for your livelihood, say so early, at the hearing, with specifics. This is not an argument that improves with time.

Is requiring a device even constitutional?

This gets asked constantly and the answer is settled, so it is worth stating plainly rather than leaving as an open question.

Texas courts have rejected challenges to the interlock bond statute on every one of these grounds:

• That it does not ensure the accused’s appearance at trial
• That it constitutes punishment
• That it constitutes a fine
• That it is contrary to the presumption of innocence
• That it violates separation of powers

The reasoning is that the device serves a narrow governmental purpose, keeping people who have been charged with intoxication offenses from driving after drinking, and that it is a less severe infringement on driving than outright revocation of a license would be. On that view it is not punishment and it is not oppressive.

You can disagree with that reasoning. It is the law, and building a strategy around a constitutional attack on the device is not a good use of anyone’s money. The productive route is the best-interest-of-justice exception above.

Testing and treatment on a personal bond

If a court sets a personal bond, it must require the defendant to do two things: submit to testing for alcohol or a controlled substance, and participate in an alcohol or drug abuse treatment or education program.

That requirement is not automatic on every personal bond. It applies where both of these are true:

• The investigating or arresting officer, or the magistrate, reasonably believes a controlled substance was present in your body, or there is a finding of drug or alcohol abuse related to the charged offense; and
• The condition will serve to reasonably assure your appearance for trial

The cost of testing may be assessed as court costs or ordered paid directly by you as a condition of bond.

Worth noting for anyone weighing whether to seek a personal bond: this is what comes with it. A personal bond is not simply a release without money. It is a release with a supervision package attached. Whether one is realistically available depends heavily on the county: see Dallas, Tarrant, Denton, Collin, and Rockwall County practice.

The protection attached to that testing

This is the most valuable and least known fact on the page.

The State may not use the results of this bond testing in any criminal proceeding arising out of the offense you are charged with.

That is a statutory protection, and it exists because otherwise the condition would function as a mechanism for the State to generate evidence against a person it has already charged, while that person is presumed innocent and has no practical way to refuse.

Two things it does not do. It does not protect you from the consequences of a violation in the bond proceeding itself. A positive test can still cost you your release. And it is specific to the offense you are charged with.

But if you are on a personal bond and someone suggests that a test result will show up at your DWI trial, that is not how the statute reads.

Home confinement, curfew and monitoring

Beyond the mandatory conditions, a magistrate has discretionary tools, and they differ depending on the bond type.

For any DWI defendant released on bond, article 17.44 lets a magistrate require either home confinement with electronic monitoring under the supervision of a designated agency, or weekly testing for the presence of a controlled substance.

For a defendant released on a personal bond, a magistrate may additionally require home curfew with electronic monitoring under a designated agency’s supervision.

Cost for either may be assessed as court costs or ordered paid directly by the defendant.

The trend in Texas bond practice is toward technology that reports closer to real time. Transdermal alcohol detection devices such as SCRAM and portable breath testing devices both require periodic uploading of data, and positive results are reported to the court. This area is developing quickly, and the direction is toward continuous rather than periodic supervision.

How interlock devices get it wrong

An interlock device is a breath alcohol analyzer wired into the ignition. You provide a deep lung sample below a preset threshold, often around 0.02, before the engine will start. Many systems also demand rolling retests while you are driving, to catch drinking after the car starts. Every sample is captured, timestamped, and stored or transmitted for compliance review.

These devices are not infallible, and the error sources are documented:

Residual mouth alcohol. Mouthwash, breath sprays, or recently swishing anything can trigger a false fail if you skip the waiting period before blowing.

Medical and physiological causes. GERD and acid reflux, chronic obstructive pulmonary disease, and poorly controlled diabetes producing ketoacidosis can all put substances into a breath sample that interfere with the sensor.

Calibration drift or tampering. A device that is not properly maintained and calibrated, or that someone tried to circumvent by having another person blow, produces logging irregularities that read as violations.

Breath sample technique. A shallow or incomplete sample can register as invalid or get flagged, which is not the same as a positive but can look like a pattern.

The records worth getting hold of are the calibration log, the pattern of invalid samples, and documentation of any medical or environmental cause. A flagged reading is a data point, not a finding.

SCRAM and continuous alcohol monitoring

Continuous transdermal alcohol monitoring, usually an ankle bracelet, measures ethanol coming through the skin. The device samples roughly every 30 minutes, converts the reading electrochemically, and transmits data to a monitoring service, where analysts apply algorithms meant to separate actual drinking from environmental contamination and to flag tampering or loss of contact.

Four technical points matter if you are wearing one:

There is a lag. Transdermal alcohol concentration trails blood or breath alcohol by roughly 30 to 90 minutes, and sometimes more, depending on hydration, skin thickness, and blood flow. A reading does not correspond to a moment in time in any direct way.

Environmental exposure registers. Alcohol-based hand sanitizers, scented lotions, and vapors in enclosed spaces can all affect readings. Combine that with the lag and there is a real scenario in which an exposure at work appears as apparent consumption at home hours later.

Devices have baseline noise. Low-level drift has to be filtered by thresholds rather than treated as signal.

The algorithm is contestable. Courts widely accept this data, but the algorithm logic, calibration history, and any analyst override are all reviewable, and an effective challenge looks at all three.

The honest framing is this: a transdermal reading is not a blood alcohol measurement. Its strength is continuity and the difficulty of timing around it, not precision at any given moment.

What a violation actually costs

If a defendant violates a condition of home confinement and electronic monitoring, or refuses to submit to a test for controlled substances, the magistrate may revoke the bond and order the defendant arrested.

That is the whole mechanism, and it is quick. There is no separate trial on the violation. You can be back in custody on the pretrial case while the underlying charge is still unresolved.

Bond conditions run for the whole life of the case, which is longer than most people expect: how long a Texas DWI case takes.

The follow-on costs are worse than the night in jail. A revocation becomes part of your history with the court, and how a defendant complied with previous bond conditions is one of the factors weighed in setting bail. Getting released a second time is harder and more expensive than the first.

This is why the next section exists. Most violations that come through are not people drinking. They are people who did not understand how the device treats ordinary products.

How to live with a device without tripping it

Monitoring shifts the risk onto you. A single false positive can cost you your release, and the burden of explaining it afterward is yours. Practical rules:

Learn the waiting periods and use them. Do not blow into an interlock immediately after mouthwash, breath spray, or anything else swished in your mouth. The wait exists precisely for this.

Give full samples. Shallow or incomplete breaths generate invalid readings that accumulate into a pattern.

Tell someone about your medical conditions now, not after a reading. GERD, COPD, and diabetes are all documented sources of interference. That is a conversation to have with your lawyer and with the monitoring agency before there is a problem to explain.

On a transdermal monitor, treat alcohol-based products as a hazard. Hand sanitizer, scented lotions, and working around solvents in an enclosed space can all show up. Where you cannot avoid exposure, note it.

Keep a written, dated log of legitimate exposures. This is the single most useful habit available to anyone on a device. A note made the day it happened, saying what you used and when, is contemporaneous documentation. The same explanation offered for the first time at a violation hearing three weeks later is an excuse. The difference between those two things is whether you wrote it down.

Know what to do the moment something flags. Contact the monitoring agency and your lawyer, document the context immediately, and do not wait to see whether it resolves itself. One flagged reading that gets explained is a non-event. The same reading left unaddressed while a second one arrives is a pattern.

Where bond conditions fit into the night of the arrest is set out in DWI jail release and bond.