Typically, UPS requires a signature from the recipient upon delivery of the shipment as confirmation that it has been successfully delivered.
In certain countries, it is possible for the shipment to be left without a signature, through the following options:
Driver Release
The shipment is left at the recipient's address (within the premises) without requiring a signature.
Letter Box Release
Smaller shipments may be left in a secure mailbox without a signature from the recipient.
Note: The availability of these options depends on the delivery country and local delivery rules.