Wiktionary
blinkenlight
n. 1 A flashing light or beacon light. 2 A status light on a electronic or electric device such as a modem, router, network hub, and so forth.
Usage examples of "blinkenlight".
The LEDs (Das Blinkenlights, as they are called in the Be community) flash merrily next to my right elbow as I hit the keys.
Some German hackers have even come up with a Das Blinkenlights replacement: it's a circuit board kit that you can plug into PC-compatible machines running BeOS.