Even though a signature isn't required upon delivery, couriers are still obligated to make a personal drop off. This means that if nobody is available at the delivery address to accept the parcel, a courier will have to take the parcel back with him. Then, your parcel will be brought to a local pickup point for you to collect and the courier will leave a card in your mailbox to inform you of this. Please be aware that if the parcel isn't collected within 5 business days, it will be returned to sender.
When you're not sure if someone will be available to accept the parcel at your home address, you can also consider using an alternative delivery address like your work address or the address of a friend or family member.