Which of the following is the LEAST intrusive?

A firmware update is highly intrusive as it involves modifying the core software of a device, often requiring reboots and carrying a risk of bricking the device if interrupted.

A remote management card, while allowing remote interaction, involves software installation and network configuration, and can be used to initiate intrusive actions like power cycles or reboots.

Diagnostic LEDs (Light Emitting Diodes) are visual indicators on hardware that signal the operational status or specific error codes of components. They are non-interactive and provide information at a glance without requiring any system changes, reboots, or physical contact with electrical components, making them the least intrusive.

A multimeter is used to measure electrical properties and requires direct physical contact with electrical circuits, which is intrusive and carries a risk of shorting components if misused.