It is not necessary that a person show signs of impairment to found a basis for making a roadside breath demand. Nor is it necessary that a police officer suspect the person is committing a crime. All that is required is that the police officer making the demand has reasonable grounds to suspect that a person has alcohol in their body.

See  s. 254(2) of the Criminal Code;R. v. Schouten, 2016 ONCA 872 at para 26.

Reasonable suspicion must be assessed against the totality of the, circumstances. 

R. v. Chehil, 2013 SCC 49,
[2013] 3 S.C.R. 220, at para. 29

The standard of “reasonable grounds to suspect” involves possibilities, not probabilities:

R. v. Williams, 2013 ONCA 772, at para. 22, citing R. v. MacKenzie, 2013 SCC 50 at para. 38; R. v. Chehil, at para. 27; R. v. Kang-Brown, 2008 SCC 18, [2008] 1 S.C.R. 456, at para 75.

In R. v. Schouten, 2016 ONCA 872, the absence of the indicia of impairment even when combined with the fact that the individual claimed to have consumed his last drink many hours earlier, did not negate the possibility that the driver had alcohol in his system, which was raised by the presence of an odour of alcohol on the driver’s breath and the driver’s admission of consumption of alcohol (albeit, an admission that his last drink was 10 hours earlier).