Canadian law describes two devices used for the detection of drunk driving offences. An "approved screening device" is a portable measuring instrument that a police officer can use to gather evidence related to blood alcohol content. If the driver fails the screening device test, a further test using an approved instrument will be used to gather evidence that is considered valid for criminal prosecution. Where the driver displays significant signs of impairment such as bad driving behavior or physical signs of intoxication, the officer does not need to use the screening device as well. In Ontario, failing the screening device can result in a temporary suspension of the driver's licence even if no subsequent criminal charges are laid.
An "approved screening device" is a portable instrument used in the field by a police officer, which is checked for accuracy at regular intervals. An "approved instrument" is used by a trained technician under controlled conditions, and checked for accuracy on each use, to produce evidence suitable for use in prosecution.
The expression approved instrument is defined  in the Criminal Code of Canada as:
approved instrument means an instrument of a kind that is designed to receive and make an analysis of a sample of the breath of a person in order to measure the concentration of alcohol in the blood of that person and is approved as suitable for the purposes of section 258 by order of the Attorney General of Canada
An approved instrument demand can be made whenever a police officer believes on reasonable and probable grounds that a person has committed an impaired or over 80 offence within the preceding 3 hours. The approved instrument breath demand should be made by the same officer who formed the reasonable and probable grounds. In order for the instrument to be approved, it must be calibrated 15 days within the time of testing. All roadside test kits must be calibrated in Ontario. The indicia of impairment leading to the formation of the reasonable and probable grounds must be apparent before or at the time the opinion is formed, not discovered ex post facto.
The Approved Breath Analysis Instruments Order establishes certain breath instruments as approved instruments for use in Canada. A breath instrument is commonly known in the United States as a breathalyzer.
It is a criminal offence in Canada to refuse an approved instrument demand that has been lawfully made. Section 254(5) of the Criminal Code of Canada provides as follows:
(5) Every one commits an offence who, without reasonable excuse, fails or refuses to comply with a demand made to him by a peace officer under this section.
The calibration of an approved instrument in Canada should be checked using a standard alcohol solution at a specific temperature using a simulator each time the operator of the approved instrument conducts a subject test.
Evidence of the results of subject tests using an approved instrument in the context of several conditions precedent presumptively becomes proof, in the absence of evidence to the contrary, that the blood alcohol concentration at the time of the breath tests equals blood alcohol concentration at the time of the driving or care or control.
-  M.J. Wilkie, J. G. Wigmore, J. W. Patrick The Performance of the Approved Screening Device, the Alcotest 7410 GLC, in the Field: Low Incidence of False Positive Results in the Identification of Drinking Drivers" Can. Soc. Forens. Sci. J. Vol. 36. No 3 (2003) pp. 165-171
-  Criminal Code of Canada section 254 (1)
-  Criminal Code of Canada section 254(3)
-  R. v. Pavel
-  R. v. Gavin
-  Canada Regulations SI/92-105, s. 2; SI/92-167, s. 1; SI/93-61, s. 1; SI/93-175, s. 1; SOR/94-422, s. 1; SOR/94-572, s. 1; SOR/95-312, s. 1; SOR/2000-200, s. 1; SOR/2002-99, s. 1
-  Alcohol Test Committee Recommended Standards and Procedures page 114
-  Criminal Code of Canada section 258 presumptions