It's common knowledge that every network interface has a media access control (MAC) address. Watchman Monitoring will report the active MAC address in its hourly reports, and via our API.
Many inventory systems, and some more expensive software will make use of the lowest available MAC Address on a Mac as a piece of the identity as it relates to copy protection. Watchman Monitoring defines this as the System MAC Address.
The System MAC Address is also displayed in the Dashboard, and included in API results. Certain plugins may also report if it changes (LightSpeed Pro, for instance).