Breath test and breath analysis: how a roadside alcohol check works in Belgium

An alcohol check seems like a simple routine: you blow, the device gives a result and the officer writes it down. Yet every step is governed by precise rules. They are set out in Article 59 of the Road Traffic Act (loi relative à la police de la circulation routière) and in the Royal Decree of 21 April 2007 on breath test and breath analysis devices. If you know these rules, you know what you can ask for and where mistakes can creep in.

This article complements our overview of drink driving.

Stage 1: the screening test

At large-scale checks, the police often first use the “sniffer”: a device that detects, without a mouthpiece, whether there is alcohol in your breath. This pre-test is not compulsory for the police, nor for you. If you refuse, you do not commit an offence, but you go straight on to the breath test.

A green screen means that no alcohol has been detected and you can continue your journey. A red screen leads to a breath test.

Stage 2: the breath test

The breath test is an indicative measurement. The Royal Decree prescribes how it must be carried out:

• the officer shows you a wrapped mouthpiece, opens the wrapping in front of you and fits it to the device without touching the mouthpiece (Article 24);
• you blow hard enough until the device indicates a valid sample;
• the officer shows you the result and reads it out (Article 25).

Three results are possible. Safe means the procedure stops there. Alarm indicates a concentration from 0.22 mg/l EAA (exhaled alveolar air) and positive a concentration from 0.35 mg/l EAA. In those last two cases, a breath analysis follows.

If you cannot blow hard enough, a new breath test or a blood test follows. A refusal can also be oral and is recorded in the police report (procès-verbal). Find out more in our article on refusing a breath test.

The 15-minute waiting period no longer exists

Previously, you could ask for a 15-minute waiting period before the breath test or breath analysis. This allowed mouth alcohol to disappear, for example if you had just had a sip of a drink. The Royal Decree of 19 April 2024 abolished this period, with effect from 1 May 2024. According to the government, current devices recognise mouth alcohol themselves.

For facts after 1 May 2024, you can therefore no longer rely on the absence of a waiting period. For older facts, the Court of Cassation had already held that failure to observe this period does not automatically lead to the evidence being excluded (Cass. 6 September 2016, P.15.1105.N).

Stage 3: the breath analysis

The breath analysis provides the legal evidence. The device gives a precise value in milligrams per litre of exhaled alveolar air. The printed ticket must be attached to the police report. If an analysis is not valid, it can be repeated, with no limit on the number of attempts.

Your right to a second analysis

Article 59, § 3 of the Road Traffic Act gives you the right to ask immediately for a second breath analysis. The officer must explain this to you (Article 26 of the Royal Decree). There must be at least five minutes between the two measurements.

It is then checked whether the two results fall within the margin of precision set by Annex 2 of the Royal Decree:

Concentration measured	Permitted difference
Less than 0.40 mg/l	0.03 mg/l
From 0.40 to 1.00 mg/l	7.5%
From 1.00 to 2.00 mg/l	15%
From 2.00 to 3.00 mg/l	30%

If the two results fall within this margin, the lower one counts. If the difference is larger, a third analysis follows. If two of the three results are close enough, the lower of those two counts. If this is not the case for any pair, the breath analysis is treated as not having been carried out and a blood test follows.

Four examples

• You blow 0.35 and ask for a second analysis: 0.36. The difference is within the margin. The result is 0.35.
• You blow 0.65, then 0.49. The difference is too large, so a third analysis follows: 0.48. The last two are close enough. The result is 0.48.
• You blow 0.65, then 0.59 and a third time 0.67. Between 0.65 and 0.67, the difference is small enough. The result is 0.65.
• You blow 0.25, then 0.30 and a third time 0.35. No pair is within 0.03 mg/l of each other. The breath analysis is treated as not carried out and a blood test follows.

The second example shows why it is worth asking for a second analysis: the result can be considerably lower. Around the 0.35 mg/l threshold, this can make the difference between a lighter and a heavier category, or between an immediate withdrawal of your driving licence (retrait immédiat du permis de conduire) and no withdrawal at all.

Stage 4: the blood test

A blood test follows in particular where:

• the breath test indicates a concentration, but the breath analysis cannot be carried out;
• neither the breath test nor the breath analysis is possible, for example in case of hyperventilation or lung disease, and you show clear signs of having consumed alcohol;
• after an accident, it is not possible to check whether there are signs of alcohol consumption;
• the three breath analyses are too far apart;
• you refuse the breath test or the breath analysis.

You can also ask for a blood test yourself as a counter-analysis, where the final result of at least two breath analyses is 0.35 mg/l EAA or more. The blood is taken by a doctor called in by the police. You can be assisted by your own doctor, but the doctor called in does not have to wait for them to arrive. Your doctor can only observe and have their findings recorded in the police report.

Where mistakes can creep in

When going through the criminal file, the following points in particular are checked:

• Is the breath analysis ticket in the file?
• Were you informed of your right to a second analysis?
• Was the result correctly determined according to the margins of precision?
• Was the device approved and calibrated on time?
• Does the description of the check in the police report match what happened?

Not every mistake leads to an acquittal. A judge only excludes evidence if the mistake affects its reliability, if the formal rule is prescribed on pain of nullity or if the right to a fair trial is compromised. A mistake in calculating the final result can, on the other hand, directly change the penalty. Find out more about the consequences of mistakes in our article on errors in the police report.

Frequently asked questions

Have your case reviewed

Have you been summoned (citation) to appear in court after a breath analysis? We go through the file with you and check whether the check was carried out correctly. Contact us.

Law as at 28 September 2026. We update this article when the rules change.