One way an intruder might easily enter your home through the front door is with a bump key. A bump key is a key that is cut in a special way that enables it to pick a pin-tumbler lock. While not every home will have this type of lock, it is still one of the most common types of lock in the world so it's worth checking to see if your doors have pin-tumbler locks.
Bump keys are still relatively easy to get hold of, generally, all you need to know is the make of lock you want the key for. Another reason bump keys appeal to would-be intruders is that it is pretty easy to learn how to use one and takes very little time and skill to master.
If you are worried that an intruder could easily enter your home through the front door, what should you do? You can install bump proof locks but these are difficult to find and expensive so you may find it easier to install bump resistant locks instead. You can also look at the other methods of home security available and see which one is right for you.