Door/Window Sensor - triggered by motion but no one there

I had my ring system set on home and in the middle of the night the alarm system went off, scared me half to death. I checked the Ring camera since it indicated it was the front door sensor that had motion but I don't see anyone at my door. We don't have pets and my kids were sound asleep. My ring camera battery was at about 15%. Will the ring camera still pick up an image with a low battery? The customer support said it might not. I asked if it was a glitch with the connector and she insists that someone/something would have had to try the door to trigger the alarm. Could it be a faulty sensor? She did a sensor reset to be sure. This has never happened to me before.