How locks become "smart"

Smart locks employ Bluetooth, Wi-Fi, or Z-Wave radio signals to communicate with apps on smart phones, Wi-Fi bridges, or smart home hubs.

Almost all smart locks have Bluetooth, and generally this is how they can be set up with an app on a smart phone. Often, these models can unlock automatically when you (and your phone) enter Bluetooth range or can be manually locked/unlocked via the app. Some of these can be accessed remotely with a separate Wi-Fi bridge that connects them to a local network.

Smart locks with Wi-Fi built-in, and connected to your home network, can be operated and monitored remotely with an app on a smart phone. They may also connect to or be integrated with security systems, smart home devices. Note that, locks with built in WiFi will drain batteries faster than low energy radio waves, like Bluetooth or Z-Wave.