An “always on, mostly off “ device or service is an entity that only takes action when it is needed.
An airbag in a car is an always on, mostly off device.
A city fire service is always on, mostly off service.
A security camera with motion detection and SMS alerts is a combined product and service that is always on, mostly off.
The idea of devices and services being always on, mostly off is an important part of the “internet of things”
Always on, mostly off – AOMO
