Let's not connect a smart lock to the cloud...
This lock can (also) be opened by SMS through a built-in modem
No internet? No problem
This lock is very robust. If the internet is down, SMS will probably still work. This way you can always remotely open the door to guests.
Not connecting it to the internet also means it's not exposed to hackers.
You can create (temporary) passwords. This is useful if you have someone who periodically needs to visit a home, for elderly care or a cleaning person. You don't need to give them a key, just a password, which you can revoke at any time.
This device can toggle two relays, so it can manage a building door and apartment door at the same time.
You can pick your own electric locks to go with it. If you building already has electric locks you could try to integrate it.
Building the Smart Lock
Connect the modem
You will also need to plug a simcard into the modem.
This modem is the one you need.
Connect the VCC_IN to one of the positive (red) pins, and the GND to any of the negative (black) pins.
Connect the TXD (short for "transmit") to pin 4, and the RXD (short for "receive") to pin 3.
Check the code if you like.
Because the modem is relatively power hungry, it needs to be connected to the power source directly. You could use two USB wires, or get a nice splitter cable like in this example. Or... you could only plug in the modem module - it will then provide power to the Arduino.
Plug in the RF-Nano Arduino
Plug the RF-Nano into its socket. The USB connector should be on the outside of the main board.
Add your new device
Visit the Candle controller and on the things page press the (+) icon. Your new creation should be available. Optionally, select which of its properties you'd like to have in the spotlight. Click on "save" to complete the proces.