What do you think of the window lock shown in the picture? This is quite standard for upper floor windows that intruders cannot reach, however on a downstairs window, it won't be good enough! This is because it is not a locking window handle. Even if your window installation is of good quality with multiple points of locking, a thief will smash the window in order to reach through and operate the handle from the inside. This is why it is very important for it to be locked with a key. It is also very important that you do not leave the key in the window handle, it defeats the whole object of locking!
Recently I attended a burglary where criminals had done exactly this - easily smashing holes in the glass to open the windows from the inside. Even though the windows had locking handles, they were either left unlocked or left with the key in the handle - an easy job for the burglar.
So, as always, make sure you are using your security devices properly so that they give the protection they are meant to give. If you're not sure about the suitability of your window locks and how they work, I can provide a free locksmith security survey in East Birmingham and Solihull to put your mind at rest.