If you need it down to the second, the usual way it’s done in buildings is with two trip beams just an inch or two apart. Then you just figure out which one broke first in order to tell the direction the person was walking. There’s some discussion of this in the micro location topic.
If you’re OK within a minute or two, and you want to use something that works well with smartthings, you just need two different devices. You have the first device change the mode, and then the second device do something different based on what mode you’re in, and that way you can pick up that direction. This only requires two pretty inexpensive devices and no special code.
Here’s one that I use:
@Kristopher also has a “wasp in a box” Microlocation system but it requires a lot more devices and significant code.
Alternatively, if you use a smart combination lock and capture the user code you get someone coming in that way, as they don’t use the code when they go out.