Stay safe
Remember the following sequence to improve your safety in the home:
Lock, Stop, Chain, Check.
LOCK: Never leave either your front or back doors unlocked even when you are in the house. If someone comes to the door, don't unlock it until you know who is outside. If you don't have a convenient window from where you can see your front door, then have a spyhole fitted.
STOP: If someone arrives at your door, and you don't know them and aren't expecting anyone, stop before you unlock any doors.
CHAIN: You don't have to open the door at all if you are uncertain, but if you do, first put the door chain or bar on. Keep the bar or chain on while you assess whether or not you want to let your visitor enter.
CHECK: If the visitor is from a utility company or some other organization, ask to see their identity card and check it carefully. Remember that identity cards can be forged, so if you are unconvinced, ask for a phone number that you can ring to confirm their identity. Don't let anyone in who has no identity card, or who seems unwilling to let you check up on them. A genuine official caller will have no problem with you being careful.
Door chains and bars
These are extremely useful devices because they allow you to take a good look at a caller before you let them in. But leave the chain or bar off while you are in the house because they can slow down your exit in an emergency. Children can find them almost impossible to undo.
Just leave your doors shut and locked, and only put the chain on if the doorbell rings.