Maybe use a railroad tie as a crossbar. If you add handles, it could double as a defensive tool if you’re strong enough!
Check out Night Lock. I’ve bought over 10 of them for different houses.
Tint the window. It’s a cheap fix that gives some extra privacy.
I have a burglar bar door in front of my regular door. If you ask me, I wouldn’t even have a window on a front door. I added a small window that’s too high to reach, about 6x9 inches. Burglar bars make people look elsewhere if they’re trying to break in. They can still get through, but it just looks tougher.
For the mail slot, mine’s blocked by the burglar door. I ended up installing a separate mailbox with a lock by the front, so it’s still accessible but secure.
You could design a bar that goes over the glass as a deterrent.
Also, add a secondary deadbolt and maybe swap out the door handle for one that’s harder to tamper with.
I installed a steel bar that goes between the knob and the door, but it might be tricky with your door type.
Door chains work, but they don’t do much. Most people could just break through them.
Make sure you have a solid deadbolt, and double-check that your hinges are sturdy. Sometimes, people can just pop the hinges out to break in.
If the door itself is plasterboard, consider upgrading it to wood.
I also put up security stickers on windows and doors. Just having those visible can make a difference.
Make it hard for anyone to get in quickly. Try hinge reinforcers, add a thick film over the window, and replace the small screws in the strike plate with longer 2 or 3-inch screws.
Honestly, I’d just replace the whole door if possible.
A reinforced strike plate with long screws is an easy and affordable upgrade.
That window kinda makes securing the door pointless, unfortunately.
Doorricade crossbars work well. They’re available on Amazon or directly from Doorricade.
Add iron and vitamins! 
If you’re replacing the door, try a solid wood one. If you still want a window, place it high up and far from the latch.
Use longer screws (2.5-3 inches) for the latch and bolt catches. This alone makes it harder for anyone, even with a battering ram, to break in.
I also suggest adding J brackets on the door frame for extra strength. Place a solid oak bar across, and you’d need a lot to force through that.
Stay safe!
Steel security doors are worth every penny. I put one on my side garage door for $130, and it took me about 25 minutes to install. Worth it!
Why does it look like a prison cell? 
Tripmine facing outwards or maybe a turret? 
Grayer said:
Tripmine facing outwards or maybe a turret?
Let’s keep it realistic here.