I heard that police disturbed burglars in a house with a PVC front door. There was no sign of forced entry.They seem to think that the burglars can put their arm through the letter box and open the lock using the handle.
Use the deadlock at night.
Could be a victim of 'Lock Bumping'
Here's a way to protect yourself from 'Lock Bumping' and an explanation of what it is.
Our house unfortunately has a PVC door which we keep meaning to change. It is easy for anyone with a thin hand and arm to reach through the letter box and push down the handle on the inside to open the door. A friend with a similar front door pointed this out and now we always lock it with the key, even when we are in, but I bet lots of people don't realise as the door locks itself when you close it so it appears quite secure.