I made a smart doorbell for cats.
It is super easy, stupid but useful for us.
Every time our cat (or the neighbor’s cat, or my girlfriend) steps on that mat the lights in the living room flash and I get a notification on my phone.
There is also another light flashing which is directly next to the window so the cat gets some feedback. Not sure if that helped training her but it worked super fast.
My cat is on the lighter side with ~3.5kg so it should work for most I guess. Initially, we had a heavy doormat on top of the pressure mat, which did not work. So I bought one of those scratch mats for cats and laid it on top.
Not pretty, but works 
You need:
- Aqara Water Leak Sensor
- Pressure Mat
These pressure mats come in different sizes. Just cut the wire from the WAY too loud alarm, connected them with the screw terminal on the Aqara Water Leak Sensor and you have a perfect little boolean sensor for someone stepping on this.
I also hot glued this and put it in a project box because this is exposed to the elements and the cable corroded and broke off after a couple of months. But you can leave it as is, depending on where you put it.
Here is the full write-up on my blog:
Happy catifying your home!