LOCK: keep front and back doors locked (with keys taken out), even when at home;
STOP: stop and think if anyone is expected; look through a spy hole or window to identify the caller;
CHAIN: put the door chain or door bar on first before opening the door, and keep it on whilst talking to the caller; (Normally when the door is shut and locked, the bar or chain can be left off to get out in an emergency).
CHECK: check their identity card carefully even if the caller has a pre-arranged appointment (close the door whilst doing this); look up the phone number of who the caller represents in the phone directory; ring to verify the caller's identity; do not use a phone number on the identity card, as this may be fake.
If in any doubt, keep the caller out!