I have five of these quartz date watches, and three cases (two for 20mm bands, one for 18mm), they are Called FORTIS CONTAINER SYSTEM , because you can use different watch bodies in the steel case (container) attached to the wrist band.
All of them have Water Resistance 50 Meters, so if you open them without the proper tools and expertise, you might damage their water tightness or worse.
If you don't use it for a longer time, you can pull the crown out, as when you set the time, that way the watch is stopped, and the battery is not drained. I did that with three of them over ten years.
The FORTIS Product IDs: 560.10.132 and 560.20.132 .