Self-storage, also known as self-service storage is a service in which storage spaces called storage units are rented by tenants, usually on a short term basis. Some facilities offer boxes, locks, and packaging supplies for sale to assist tenants in packing and safekeeping their goods, and may also offer truck rentals. The rented spaces are secured by the tenant's own lock and key. Unlike in a warehouse, self-storage facility employees do not have casual access to the contents of the space and, thus, the facility is generally not liable for theft. A self-storage facility does not take possession or control of the contents of the space unless a lien is imposed for non-payment of rent, or if the unit is not locked the facility may lock the unit until the tenant provides his/her own lock.