Among the various technology gizmos I’ve seen at the UK, this is the best. Our flat has a security system that does not allow anyone without an electronic key to enter. As with most flats, there is a panel on which you can dial the flat number and speak to the owner. Usually this is connected to an intercom in the flat. I was initially surprised that there was no intercom in our flat.
It turns out, you can program the system to dial your mobile phone or land line. So when I’m at office, I get a call from the “House Door Panel”, as it identifies itself. I speak to the person at the entrance, press 0 on my phone, and the door automatically opens! In fact, this is how I let myself in when I don’t have keys.