Holman Engineering has developed many High Level Interfaces. High Level Interfaces allow two or more systems to communicate with each other (usually through a serial or TCP interface). Holman Engineering has interfaced to many security systems including the widely used Pro-Watch system. Examples of HLI's that have been developed by Holman Engineering are:

- Lift Interface: Allows a security system to interface to a lift controller. This restricts access to certain floors for users.

- Keysafe Interface: Allows a security system to interface to a keysafe. This restricts which users can get access to certain keys. It can also block users from exiting a building or area if the user has keys out. This interface is used in many prisons around Australia to ensure no staff leaves the prison whilst they have a key in their possession.

- Prisoner Movement System: Allows a security system to be used to restrict prisoner movements around a gaol.

- CCTV Camera Interface: Allows a PTZ (Pan/Tilt/Zoom) camera system to interface to a security system. This allows cameras to be automatically moved to show a certain location when a security event occurs (ie a card is read at an access point).

- Time and Attendance System: This software interfaces to a security system and generates reports and data suitable for importing into payroll packages (eg Sybiz Visipay).