Err starts up in 2 different ways: When powered up in a lighted environment: Install batteries and Err will blink on 5 times and then turn off until exactly 90 minutes past dark, when he will automatically turn to "constant on" until daylight again. When powered up in a darkened environment: Install batteries and Err will blink on 5 times and then turn "constant on" for another 30 seconds and then turn off for 90 minutes. Then he will automatically turn "constant on" until daylight again. He must remain in darkness for the full 90 minutes or the 90-minute timer may possibly reset itself if exposed to light. Photocell is located on lower left hand corner.