You can always break in somewhere given time and tools. But like the old saying goes, you don't need to overrun the tiger, you need to overrun the other guy.
If a robber has to choose between a locked door and an unlocked door, they will chose the unlocked one. I used to live in an apartment with a door that was so bad that the previous tenant had to add a second lock just to keep it closed, but one day a burglar came and robbed my neighbor. Discussing about why they chose his rather than mine he noticed "from the outside, it looks like you have hardened your door with a second lock".
And yes, you can break windows (if you have easily accessible windows) but a broken window is a much clearer sign of something going wrong than an opened door.
If a robber has to choose between a locked door and an unlocked door, they will chose the unlocked one. I used to live in an apartment with a door that was so bad that the previous tenant had to add a second lock just to keep it closed, but one day a burglar came and robbed my neighbor. Discussing about why they chose his rather than mine he noticed "from the outside, it looks like you have hardened your door with a second lock".
And yes, you can break windows (if you have easily accessible windows) but a broken window is a much clearer sign of something going wrong than an opened door.