Step 1: While standing in the garage, block the electric eye near the floor and press the button to close the door; it shouldn't budge.
Step 2: Lay a two-by-four on the ground across the door opening and close the door. When it hits the wood, it should reverse.
If the system fails either test, repair or replace the opener ($200 to $400 a door).
Frequency: Once a year.
Last updated December 20 2007: 9:44 AM ET