Largely responsible for this development is the computer that enables access control devices to create systems of tremendous power and flexibility, incorporating functions that in the past required several separate systems. As a result, the security office has been transformed into a high-tech area with vital information instantly available to the security staff, as well as a place from which security professionals can control and manage facilities in an efficient manner. In a card-based system, the card reader reads the data on the card, transforms this data into a number, and sends it to a control unit (an ACP -- access control panel). The panel analyzes the number and verifies that all conditions to grant access are satisfied before the door is released. To increase the security level and flexibility of such systems, many manufacturers are adding a keypad to the card reader, requiring the user to use both a card and a code to gain access. Other developments include programming the access control system to let in only a certain number of persons in areas monitored for loading, and using cards, pins, biometric devices, and even scales to weigh users and their belongings.