Dragon Age: Red Daughter
Signal Spheres are an ancient Elven magical technology. An enchantment links two glass objects, traditionally spheres, but they can be any shape.
If one of th Signal Spheres is broken, the other is triggered, and begins to glow brightly. The glow lasts for approximately an hour, or until the remaining sphere is broken.
They were used for simple, long-term communication, to alert of approaching danger.
The Keeper retains the knowledge of how to create Signal Spheres.