Block entry points: Inspect your home for openings that rats may use. Seal them with steel wool or caulking.
Remove sources of attraction: Store your food in airtight containers and be sure not to leave crumbs or trash lying around.
Protect your pets: Be careful, onions are toxic to cats and dogs. Place them out of their reach.
Why choose onions over chemicals?

Economy: onions are much less expensive than commercial poisons or traps.
Safety: no risk to your health or that of your children, unlike chemicals.
Availability: no need to look far, onions are already in your kitchen.
When to call a professional?
Although onions are very effective, they may not be enough in the event of a severe infestation. If rats persist despite your efforts, it is time to contact a pest control expert for appropriate intervention.