Rats are very secretive and sneaky creatures and, as such, they're not often spotted. However, evidence of rats can be easily detected. Rat droppings, nests, burrow paths, gnawed wires, and scattered garbage may be indicators of a rat's presence in your garage. There are various methods of rodent population control to help trap the rat before the damage and rat population get out of hand.
Identify places where the rat has been. Rat droppings, boxes with gnaw marks, and bits of fur are indicators of a rat's presence. Roof rats commonly travel along garage beams when coming down to look for food.
Choose a method for trapping the rat. People commonly use classic spring-loaded traps to trap rats and mice. More recent traps have large plastic treadles and don't require baiting. They work when the rat walks through the trap on its hunt for food, triggering the treadles to spring closed and trap the rat. Glue traps are also effective in preventing the rat from going anywhere once it has attempted to retrieve the food.
Bait your trap if necessary. Bacon, nut meat, cheese, and dried fruit all make good bait. Peanut butter and cream cheese also attract rats, but rats might be able to retrieve soft bait without triggering the trap. Use a bit of glue or string to secure the bait to the trap.
Place the trap in the infested area and wait. Put the trap into an area you identified in Step 1.