Here is another method that may help also.
Take F/T or live (bait) whatever yours eats, Put it in a aquarium with screen lid on it so the smell of the rat can get out. Then just get some plastic cups and put some coins in them and place them on top of the tank and or around it. Trust me it will Knock one of them over and wake you up.
You can variate the method to suit your needs.
You can also put cups of coins around the walls of the room since this is usually where they like to travel. Much like the plastic bags Ash mentioned, I just find that a cup of coins hitting the floor will pretty much wake the dead.
Good hunting :)