Below is an example of such door, where there is no handle that you can twist. There is only a fixed handle, and a place to insert the key to lock the door.
The question. If you leave the house, with the door unlocked, and decide to re-enter the house without having the key, then how will you open the door? With a classical door, you rotate a moving handle. But with these, the handle doesn't seem to be rotateable.
I have doors like these that are closed and locked by a deadbolt.
Per the other posters, the lock is a deadbolt, which uses a key on the outside, and the inside can either be a key or knob. If you leave the house without a key, it cannot be locked except from the inside.
The door is kept closed when unlocked, by devices such as these Ball Catch. These ball catches are placed on the top edge or the opening edge to provide fiction to hold the door close.
In a heavy wind, the door may still be blown open
per the other question -
The question. If you leave the house, with the door unlocked, and decide to re-enter the house without having the key, then how will you open the door? With a classical door, you rotate a moving handle. But with these, the handle doesn't seem to be rotatable.
The door is held shut by the catch ball, to open you just push on the handle or door.
Some doors have no latch-handle on one side requiring a key to be used to retract the latch.
The question. If you leave the house, with the door unlocked, and decide to re-enter the house without having the key, then how will you open the door? With a classical door, you rotate a moving handle. But with these, the handle doesn't seem to be rotateable.
If you latched the door behind you then you are out of luck and need to call someone on the inside, find a (person with a) back-up key or call a locksmith. With a door like that you should have the habit of always having your keys with you to avoid that scenario.
If you want to leave the house without a key and reenter later then you need to prop open the door with a door-stop to prevent wind from slamming it. Sometimes you can leave the door resting against the latch but a strong draft can still overcome that resistance and latch it closed.
My guess is that if the door was not lucked by the key, a push-button will retrieve the tongue to the unlocked position, a slight blow of air will open the door. If it is locked by key, the button is locked as well.
