This term refers to any device or system that selectively allows entry by certain persons to an area while excluding others. Usually, this term is not used to refer to ordinary key-operated locks but rather to push-button, card access, or biometric systems. This can be anything from a simple mechanical push-button lock to retinal scanners, palm scanners or badge readers wired to magnetic or electrical locking devices. Many professional locksmiths offer access control services and can advise you on the best system for your particular application.