An Approved Screening Device is a handheld breathalyzer used by police at the roadside to test whether a driver has alcohol in their body. The ASD gives one of three results: pass, warn, or fail. A "fail" result gives the officer grounds to arrest the driver and demand a more precise breath test at the station on an approved instrument.
Since Bill C-46 came into force in 2018, police can demand an ASD sample from any lawfully stopped driver under section 320.27 of the Criminal Code — they no longer need to suspect the driver has been drinking. This is known as mandatory alcohol screening.
ASD results are not used as direct evidence of blood alcohol concentration at trial. Their function is to establish reasonable grounds for arrest and for demanding a breath sample on the station's approved instrument. Defence counsel frequently challenge ASD demands where the stop itself was unlawful or where the officer failed to comply with the operating requirements of the device.