A breathalyzer — formally an approved instrument — is the device used at the police station to measure a person's blood alcohol concentration (BAC). Unlike the roadside Approved Screening Device, the approved instrument produces readings that are used as evidence at trial. The results are recorded on breathalyzer certificates, which are presumed accurate under section 320.31 of the Criminal Code.
The accused provides two breath samples, typically about 15 minutes apart. If either reading is at or above 80 milligrams of alcohol per 100 millilitres of blood, the accused will be charged with "over 80" under section 320.14(1)(b). Defence lawyers challenge breathalyzer evidence by examining the calibration records of the instrument, whether the qualified technician followed proper procedures, the timing of the tests relative to the last drink consumed, and whether the accused's right to counsel was respected before the samples were taken.
The distinction between the roadside ASD and the station breathalyzer is critical in impaired driving defence. Errors at either stage can provide grounds for excluding the evidence under section 24(2) of the Charter.