The Pool And Pond Remote Temperature Display
This sensor floats in your swimming pool, hot tub, or Koi pond and wirelessly reports the water temperature to a remote display in your home. The floating sensor can send a signal up to 300′, allowing you to place the display anywhere in your home without interference.
These gadgets would be great for monitoring the hot tub temp without having to trudge back and forth every 15 minutes to see if it is up to or —oh no — over temp.