For the second option, there are currently two different “robot fingers” which can be easily added to Push the Button. Both integrate with SmartThings through the free IFTTT service. Both use Bluetooth, not WiFi, which is what you’d expect since WiFi devices have terrible battery life. Both offer a separate plug-in Bridge device to connect to your WiFi and get to IFTTT that way. As of 2018, Both have a cloud component.
The first is from a South Korean engineering company, Naran. They offer the Push Microbot. It has been available for almost two years and the hardware is very well-engineered. I use these in my own home. The app is full featured but not user friendly. They have made continual hardware improvements in new generations, and the app has gotten a little better over time. It used to be that the biggest downside was the cost, but in late 2017 they decided to add a required cloud component AND an annual subscription charge, so now I mention it for completeness, but I don’t directly recommend it. These are sold on the company site or at Amazon.
The second is from a Japanese consumer products company, Wonder Tech. It is called “Switchbot.” It is less elegant and much cheaper looking, very “cutesy”. It costs less, with no subscription and a much more intuitive app, but with fewer features. The design will fit fewer devices than the Naran because of the way the “finger” part is designed, but it should still fit a lot. I have some on order and expect to test them in May 2018. I believe as of this writing the only way to buy them is through the company.
You could also do the same thing with an ESP8266 and a relay. What is the voltage coming out of the buzzer? If it’s between 5 and 12, you could even run the board off the buzzer as well, as these are very low power boards. It all depends on how much modification you’re willing to do with the intercom that you’ll either have to pay for or put back when you move out. Take a look at the ST_Anything project.
Very true but keep in mind that the 24/110 power doesn’t have to be at the intercom. You just need a small gauge wire to the button and can run it to the relay. For example I have my Qubino in my crawl space 15 feet away from the button it is controlling.