A large hole for putting your hand through the door, and a knob on the back to open the door. Above the hole on the hinge there is an ax which will cut off the thief's paw as soon as it touches the knob. For you, the hole in which you insert the rod that blocks the ax from falling (so that it does not cut you off

). And you're done.
Seriously, there is no way to secure it. If they try to break in, they'll break in. If it's a basement in blocks of flats from the '80s and 90s, then there is not much to protect. As such, the solution is to buy
a padlock that has no shackle, only a pin - it's hard to wring it because there is nowhere to put the crowbar.
Second thing: if the basement door is made of slats, it is obligatory to upholster it with fibreboard; you can't see what's inside. Over the door too.
Another thing is the replacement of the metal sheet that you "fasten" with a padlock - you do not have to dangle on the staple, but it has to be cut and fitted thick steel angle fixed to the door rigidly (!) Without the possibility of tearing off (the lock bolts and nuts from the inside are countered against each other ). Only by locking such an angle with a padlock will you make it impossible to tear the padlock out of the wall. Why an angle bar and not a flat bar? Because you cannot bend an angle bar with a crowbar, and a flat bar you can.

The most important thing is not to give the thief a chance to show off (no slack, no places where you can put a crowbar, etc.).
It is also good to strengthen the hinges and screw a block to the door from the inside, which will prevent it from breaking off the hinges - they are to rest on the upper edge of the door frame.
Unfortunately, there is no method for a thief, but you have to make it as difficult as possible. If he wants to get in, he will get in and you will blow your compotes

. Ev. set up an alarm that will howl in the basement and in your apartment.