Yesterday morning around 5 AM, our kitchen clock fell off the wall. We have no idea why it happened, other than the possibility that the screw it was resting on worked itself far enough out of the wall over time, due to vibration from vehicles passing by outside, that the clock finally slipped off.
What's more strange is that neither of us heard it hit the floor. The fans add white noise and if both of us were deeply enough asleep then I guess we might not hear a crash two rooms away. The Mrs. discovered the aftermath when the dog woke her to go out.
We also now know that the lens covering the clock's face was made of glass, not plastic, which seems like an odd choice for something that could potentially fall and be smashed. However, it does appear to have been a safety glass like what's used in car windows, because the broken pieces were small and not jagged like you get when you drop a drinking glass.
I cleaned up the mess and replaced the battery, which had been dislodged in the fall (which is how I knew what time it had happened), and the clock started running again just fine, as it has for the past dozen years or however long we've had it. It no longer has a lens covering the face, but so what? It's still keeping time.