The bang went off around 6:40 in the morning, and the dog still hasn't come out from under the bed.

The storm passed through overnight, hail rattling the roof and the truck hood for a few loud minutes before it moved on.

Two torsion springs built for the same door can sit side by side on a parts rack and still be rated 15,000 cycles apart.

The garage door goes up from a tap on a phone screen, and somewhere behind you a family member is holding the actual clicker that came with the opener, wondering out loud why anyone would set up an account and an app for something a button clipped to a visor already does.

The maintenance schedule most warehouse doors run on was written for a different door. Residential guidance assumes a door that opens a handful of times a day, hangs in reasonably clean air, and spends most of its life sitting still.

Count the ways into an attached two-car garage and the honest number is usually one: the big sectional door itself, lifted every day by a motor that most households never think about until it stops.

The garage portion of a home inspection report is usually short. Four or five lines, sometimes a photo of a sensor bracket hanging at an angle.

The keyed cylinder on the outside of a garage door is a release for the opener.

Most people find out whether a garage door's safety system actually works only when it doesn't: a stalled cycle, a straining motor, a door that pushes through something it should have stopped for.

You come back to a door standing where you left it, with a scrape across the bottom panel and a corner that no longer sits flat against the frame.

Ask most homeowners what makes a garage door opener "smart," and the answer comes back the same way almost every time: it has an app.

You come back into the garage, and the door is not where it should be.

Above the opening, running the full width of the door, is a steel tube. It carries the torsion springs that make a heavy sectional door feel almost weightless as it goes up.

A photo-eye protects one line. An emitter on one side of the opening sends an infrared beam across to a receiver on the other, and the operator watches that beam the whole time the door is closing.

A garage door should rise straight and sit square in its opening. When it starts going up crooked, tilting to one side, or sitting unevenly, the balanced system that lifts it has developed a problem on one side. Understanding what knocks a door out of level helps you catch it before the door binds, jams, or fails.

The assumption sounds reasonable enough: pick the biggest name on the box and reliability follows automatically.

A loud bang from the garage is startling — many people describe it as sounding like a gunshot or something heavy falling. When it comes from the garage door, there's usually a specific and important explanation, and it's one worth understanding because of the safety implications. Here's what that bang most likely means and what to do about it.

It's a stubborn problem: the garage door comes down most of the way, then stops short of the floor and rolls back up. The door isn't broken so much as it's protecting itself — modern openers reverse the door when their safety systems sense something wrong near the bottom of the travel. Tracking down what's triggering it is how you get the door to close all the way again.

A garage door that opens the morning after a storm has passed exactly one test: the opener produced enough force to move it.

A storefront security door has to do two jobs that pull in opposite directions. Closed, it needs to be hard to get through.