As a disciple of the Church of Cupertino, I believe I'm supposed to have disavowed the LED and accepted the purity of visual silence and having to guess whether a device is on or off by prodding it and seeing if it bites. I don't want to have risk my toesies in the shower. They're terribly sensitive thermostats. Plus we have a vintage boiler of uncertain temperament at the Asbestos Palace.
Anyway, if that blade of light starts to swish backwards and forwards you've got a first generation Cylon (if I remember my Battlestar Galactica correctly).
The downside is that I expect other showers to behave. I remember being in Africa earlier this year, in some place that had a lot of consonants but not a lot of hot water (according to the sign the water was courtesy of Scotland, so give them a hand, they've finally figured out what to do with all that rain). Anyway in the blissful few seconds of heat I opened my mouth for a celebratory gargle. Then I remembered it was African death water and had to hop around spitting it out like I was faulty fountain, while at the same time the water dropped to a temperature that suggested it was actually being pumped all the way from Kilmarnock.