Position a piece of foil large enough to wrap the brisket fully inside a 6 quart slow cooker.
Put brisket in the middle of the foil then add onion soup mix, garlic salt, celery salt, bay leaves, Worcestershire sauce, and liquid smoke.
Wrap the brisket securely with the foil and put on the lid. Cook on low for 8 to 10 hours or high for 4 to 6 hours, or until very tender.
Remove from foil and allow the brisket to rest for 5 minutes before slicing against the grain. Spoon the cooking juices over the sliced meat before serving.