Vase Alarm (3.5e Equipment)
From D&D Wiki
For when you don't have a handy alarm spell, a poorly balanced vase or pot makes a fine improvised alarm. The pot could be set leaning against a door that, if opened, causes the vase to fall and smash. It could also be tied to a trip wire or on the edge of a table. I would treat the DC to hear a falling vase to be 0.