The majority of smart locks are designed to work with your deadbolt; most are deadbolt replacements — that is, in order to install the smart lock, you must completely remove your deadbolt first. A few others (most notably the August smart locks) are deadbolt adapters, which requires you only to remove the part of your deadbolt that's inside your house.
There are pros and cons to each; a deadbolt adapter is generally easier to install and lets you use the keys you already have, but if you want to be able to open your door using a keypad, you'll have to purchase and install that separately.
A deadbolt replacement, on the other hand, will take longer to install, but typically has a keypad, fingerprint reader, or some other entry mechanism built into it.
Lever smart locks are also becoming more common; however, we recommend these only for use on interior doors, such as the door leading from an attached garage into your house.