The first couple of times your cat goes out from the new house is the worry, so here's a little routine you might like to try. Feed your cat at a regular time, and just before you put the bowl down, tap on it with a spoon a couple of times, and call the cat's name. After a few days of this, let your cat out just before meal time, so he will be hungry, and then stand at the door and tap the bowl and say his name - he will associate the return to the house with food, and this will encurage him back if he's wandered off. A couple of times, and he should be secure enough to come back of his own accord when ever he goes out.