Security
The garage is the easiest way into most houses, and the two methods used most often do not involve forcing anything.
Short answer
The two common methods are fishing the emergency release cord with a wire through the gap at the top of the door, and the unlocked interior door from the garage into the house. Both are addressed for very little money. After that: a side lock, a modern opener with rolling code, and not leaving a remote in a parked vehicle.
The release cord
Every opener has an emergency release that disconnects the door from the carriage so it can be lifted by hand.
On many installations that handle can be hooked with a wire pushed through the gap at the top of the door, and the door then lifts manually.
It takes seconds and leaves no damage, which is why it is common.
Shorten the cord so there is no handle hanging low enough to catch, leaving just enough to reach from inside.
Or fit a shield over the release mechanism, which is the manufactured version of the same idea.
And whatever you change, verify the release still works for you before relying on it, because that is a genuine safety function.
The interior door is the real one
That interior door between garage and house is usually left unlocked, usually a hollow slab with no deadbolt on it. Once somebody is in the garage with the door down they have privacy to work on it. A solid exterior-grade door with a deadbolt and three-inch strike screws on that opening is the single best fix on this page.
The rest of the list
A side lock or a track lock on the garage door for when the house is empty for a period.
A modern opener with rolling code security, because a fixed-code unit can be captured and replayed.
Never leaving a remote clipped to the visor of a vehicle parked outside, which is the most common way a garage gets opened.
A keypad outside and the remote kept in the house, or the vehicle built-in button.
Clearing the opener memory when moving into a house, which clears codes for remotes you have never seen.
And covering or frosting any garage windows, because what is visible inside is part of the decision somebody makes.
The things people get wrong
Relying on the opener alone as the lock, which it is not.
Fitting a side lock and then forgetting it, so the opener fights it and strains the door.
Leaving the garage door open while out of the house, which is how a substantial share of garage thefts actually happen.
Assuming a smart opener is a security upgrade, which it is a convenience rather than a lock.
Leaving the interior door unlocked because the garage door is closed.
And leaving tools, bikes and equipment visible from the street through an open door or a window.
Common questions
Can a garage door be opened without a remote?
Frequently by hooking the release cord with a wire through the top gap.
What is the best single fix?
A solid door with a deadbolt between the garage and the house.
Is a smart opener more secure?
It is a convenience. The lock and the rolling code are what matter.