The Seat Belt!

An off-duty police officer, familiar with radar guns,
drove through a school zone within the legal speed limit
when the flash of a camera went off, taking a picture of
his license plate.

The officer, thinking the radar was in error, drove by again;
even more slowly. Another flash. He did it again for a third
time, at an even slower speed. Same result.

"This guy must have screwed up the settings," the off-duty
officer thought.

A few weeks later, when he received the violations in the mail,
he discovered three traffic tickets:

Each for not wearing a seat belt!