If you have forgotten something and have to go back into the house for anything at all - whether it is to switch the lights off or go and get bus fare, or get one glove or your purse, or update your facebook status, ALWAYS, keep hold of the key.
It is so easy, when your thoughts are elsewhere, maybe already at your destination, to put your keys down absentmindedly. But, the second that the front door closes, you will immediately remember that your keys are still in the house.
Better than this, as long as you live in a safe area, if you have forgotten something, open the door and get into the habit of leaving the key in the lock. When this becomes a natural habit, then you will never have to be worried about being locked out again.
