When changing lanes you can check your blind spot by?

The best method of checking blind spots when changing lanes is to first learn where such blind spots are, and then to turn ones head, and look.

Motorcyclist in the UK are taught to look over their shoulder and make a "Lifesaver look" in the direction they intend to turn/change-lane.

Failure to look would result in a failed examination when attempting to qualify-for a motorcycle-driving licence.