Additionally, you can't use electricity on the Sabbath [0]. Unless you come up with some very clever way to couple sunlight or candlelight (!) into the fiber-op

Additionally, you can't use electricity on the Sabbath [0]. Unless you come up with some very clever way to couple sunlight or candlelight (!) into the fiber-optic cable and then detect time of flight in a non-electronic and cheap way, then just going out and checking by eye is the best bet. Great idea though! I'd always thought that looking at the phase of an electroni impluse would give you a good idea of how far along the path a break occurred, as the return signal's phase should be inverted at the break point and you can then use time of flight to infer the distance of the break. [0] This is a hyper deep part of jewish law and there are many exceptions. Please consult your local rabbi before taking my word for anything.