The Standard Field Sobriety Test (SFST) used most commonly in Canada are :
The Walk-and-Turn test is when a person must walk heel-to-toe in a straight line.
Horizontal Gaze Nystagmus Test. Despite a scary name it is a simple eye test, the stopped person must follow a moving object with the eyes to determine characteristic eye movement reaction. If the person is sober, he or she will be able to track the object smoothly, if not the eyes will jerk as they follow the object.
Finger-to-Nose test. The suspected person must tip head back; close the eyes closed and touch the tip of nose with tip of index finger.
While balance plays a major part, it is not the only deciding factor. Failing these tests would put you in front of a Drug Recognition Expert (DRE) who would perform 11 more tests to determine if your impaired by a drug. If after all of these tests the DRE is of the opinion your ability to operate a motor vehicle is impaired by a drug a blood or urine sample demand is made by the DRE.
A test by an approved instrument will also be administered to rule out the possibility of alcohol impairment.