I need to tickle ya'lls collective brain. I know what a panic snap is.... I'm kinda looking for something that can hook on a loop of rope or line and hold it but when the line goes slack it needs to release.

Imagine lowering a bucket to the ground from the roof. A hook that holds the bucket until it touches the ground. when the line goes slack, the hook releases.

The rule is... single line. A panic snap would require a 2nd small line to pull the release.... that's not gunna work....

What ideas do we have?