An obstruction detection system for motorized window shades is presented having a motor, shade material, a bottom bar, and a motor controller having a microprocessor. The microprocessor is configured to detect when an obstruction has been encountered when closing the motorized window shades. When an obstruction is detected, the microprocessor stops lowering the shade material and the bottom bar thereby preventing further damage or destruction. The system may also be used to report when an unexpected obstruction has been detected.