HOW TO OPEN MAIN DOOR of an apartment USING INTERCOM KEYPAD if you lost your keys?

Call your neighbor and have them buzz you up. If you're wondering if there's a way to hack an apartment's intercom keypad, I'm sure there is, but it's probably illegal and you'd probably be on camera doing as much. The other thing you can do is call the property manager and see if there's a way to get a replacement key..