This is a SwitchBot contact sensor. The retail price was 2980 yen. I used it for about a year, but I haven't been using it much lately, so I'm selling it. * There are almost no scratches on the outside, but one of the tabs on the back battery cover is missing, so you will need to reinforce the cover with tape or something to secure it. Therefore, please refrain from purchasing if you are concerned about this.