Right now Amazon has the Coleman Cable 9347 Indoor Safe Tree Extension Cord for $6.85.
The Safe Tree cord is a somewhat bizarre product. It is presumably a mercury switch in an extension cord. The box is lashed to the tree and if the tree falls over power is cut off. It’s certainly a dream product for those of us who worry too much, although we can’t really see how a falling tree will cause a problem electrically. Unless it falls in the pool. In which case the switchbox will get wet anyway. But we can think of other tools or products that could benefit from this, and it is certainly a cheap “hackable.”