This measures soil conductivity which correlates to how wet the soil is. It’s a simple device that just works. I compared it to a different moisture meter I had and it was within 1 unit so reasonably accurate too.

It’s a great thing to have to avoid over or underwatering your plants.

It’s currently available for $7.89 from Amazon: http://amzn.to/1QapYgZ

Full Disclosure: I received this product for free or at a discount in exchange for my honest review.