Are the Tools always working?
It seems to me that they are, though in my own experience they are far more effective when we interact with them. Cal Garrison in her book about Slim, described the rings as a direct line to the universe, in other words they carry our intentions. They are clearly aerials (compare them to the circular aerials old portable TVs had) and resonate at specific frequencies. Radio and TV use carrier waves to transmit information and I suspect that the rings work in the same way. So a Harmoniser left running in the corner will be doing a good job, but interact with it (think pushing a child on a swing) and you'll get much more out of it. The soundrepeater is a great device (and I use one at home), but having to regularly turn on a CD forces us to interact more.
I also get the sense that we won't ultimately need the Tools, but that they hold beneficial frequencies and support us in the same way stabilisers on a bicycle do when we're young. One day we won't need them and we'll be able to hold those frequencies ourselves all the time. In the meantime, they are proving to be valuable in keeping us healthy and on track in our hectic modern world.