What makes many people terrified of getting rats in their home is they can get into virtually anywhere they want to -- the sewer, the attic, in the walls, in and around garbage bins, as well as in your garage. More so, eliminating rats can be a herculean task if it's not handled with the perfect information and methodology.
Rats get to a garage through pipes, floor vents, or most often, through the doorway bumper at the ends of the garage door. These don't quite extend all of the way to the ends, and the consequent difference is often capitalized on by small animals like mice, rats, and lizards.
Rats are even more fond of the garage as an ordinary garage is full of hiding places; stashedboxes, bikes, tools, summer toys, etc. The singular best way to keep rats out of your garage would be to block their entrance into the garage. With no opening to squeeze through, there would not be a rat to remove. Traps are an excellent and efficient way to eliminate rats living in your garage. There are several kinds.
One-way exclusion funnel: All identified rat entrance holes into the garage should have been identified and sealed off except for one (and it should lead outside) before setting this up. Set the funnel over the one remaining entry point and carefully fix it on the mouth of the opening. When the rat goes out through it, it would be not able to return inside. After successfully removing the rodents, then proceed to seal off this one last opening to avoid any re-entry.
Glue Trap: It is made up of a very strong adhesive to which rats become stuck by their paws whenever they try to walk it over. Place a lure in it and put several glue traps throughout the garage. Don't forget to check regularly, so the rat doesn't remain stuck to the glue trap for hours, days or even weeks, eventually dying inhumanely of thirst and hunger.
Snap Traps: The trap goes off when a rodent steps on its trigger plate, usually drawn by a hot bait; the spring system is discharged, snaps and kills the rat instantly.