Some of them (couriers) do delivery onto doorstep when nobody is home, or if they don't have a time (see next). Someone could ask "and what about a signature ?". Huh.. signature, you say... is it that thing you can unreadably put down on their electronic gadget ?

No problem, they do it "for you" (without your permission, of course) .... and then.. well.... you might find your parcel, or not - depends on the city..
Some of them even don't bother to knock or use doorbell, because they have no time. They must eat, go to some break, do some Very Important Things, or just rest, whatever. So if you are lucky, you receive a note card; if not - they dump a parcel into doorstep and "kindly do paper thing for you", I mean sign themselves as it were your signature.
The worst thing such "types" can do - is take not insured delivery (steal it) and you might do a compensation for upto 39 pounds. I've lost memory (worth >39) sent a month ago in this way.
And once I was waiting for a 14" TV. Not LCD, but old CRT (heavy one). Courier came - I saw her through the window, lugging massive box. When I opened door for her, she just plumped it into floor with noticeable "ohmygoshhh" and gave me papers to sign ?-/ Of course, TV had kinescope ramed inside and was unusable....