This incredibly simple technique taught in driver’s ed in the Netherlands needs to be adopted in the US as standard operating procedure every time you exit your vehicle.  If you have ever accidentally doored someone or been doored yourself, you might understand the dire and avoidable consequences of mindlessly opening your car door into bike traffic.
Please share this around with your friends, especially if you know someone who is just getting behind the wheel, its much easier to establish a habit if its taught from the beginning. Stay safe out there!