I often use tripwire hooks as decorative items.

When placed next to a wooden door, as seen in screenshot, the hook randomly sends out a redstone pulse causing the door to shut.

Only happens with wooden door, when door is opened.
Is not time-related, e.g. it happens once every x seconds/minutes, but happens randomly.

Note: the tripwire hook is used as decorative item, no strings attached to it to trigger a signal.