Approved Screening Device (ASD)
An Approved Screening Device, or ASD, is a handheld breath testing instrument that police use at roadside to screen drivers for alcohol. ASDs are listed in regulations under the Criminal Code, and only listed models can lawfully be used for screening. The ASD produces one of three readings: PASS (below 50 mg per 100 mL of blood), WARN (50–99 mg), or FAIL (100 mg or higher).
Mass Tsang's DUI lawyers examine every detail of the screening procedure in roadside-stop cases. For more, see our blog post on how police use roadside screening tools in Ontario.
When ASD demands are made
Under section 320.27, an officer can demand a sample where they have reasonable suspicion the driver has alcohol in their body. Since 2018, mandatory alcohol screening under section 320.27(2) permits a demand from any lawfully stopped driver with no suspicion required, provided the officer has an ASD on hand. The driver must comply forthwith — typically within a few minutes.
What a FAIL means
A FAIL reading provides the officer with reasonable grounds to believe the driver has committed an over 80 offence and to demand an evidentiary breath sample at the police station — taken on an Approved Instrument by a qualified technician. The roadside ASD reading itself does not prove BAC at trial; only the station-house readings do. The ASD is an investigative tool that supports the next step.
What a WARN means
A WARN does not give grounds for a criminal demand, but it triggers Ontario's administrative warn range penalties under the Highway Traffic Act — immediate licence suspension, vehicle impoundment, and reinstatement fees. Repeat warn-range incidents escalate the consequences sharply.
Challenges to ASD use
Defence challenges to ASD use commonly examine: whether the underlying stop was lawful; whether the officer had an ASD readily available at the time of the demand; whether the demand was made forthwith and the sample taken forthwith; whether the device was properly calibrated and maintained; and whether the right to counsel was implemented correctly after grounds arose.
Related glossary terms
