This is a very cool gadget for all indoor plants people, and work outdoor as well. The only bad thing about this device is that, it is bare naked, meaning if you water on top of it in a long run it will oxidate, in other word the electronic components will deteriorated and will not longer work, but you can take it out every time you re-water the plant pot or just get a protection covering like a test tube that way you can water over it no problem.
So the way this work is pretty much automatic, simply insert battery, stake it to the ground or water. Then when soil if dried or water is empty to certain level, it will chirp, however it will only chirp repeatedly when there are light that way if you have this in your bedroom you do not want it to chirp while you’re sleeping. Cool huh. The best thing is it only cost about $6 on ebay. Search for “Plant watering alarm soil moisture sensor chirp when soil is dry included 3v bat” or click here https://www.ebay.com/itm/233608606786