These exist, they are called Trip beams. Most garage doors use them to determine that the space is clear. They are also used in people counter devices. They’ve been discussed in the past a couple of times, Dakota make some which are used for driveway alerts. Integration with smartthings is usually a little goofy, but can be done.
I’m pretty sure they were discussed in one of the two threads I just linked to.
OK, yes, trip beams were mentioned, but only briefly in previous link. The following thread discusses them in detail.
Some people call them “laser beams“ probably because they look like laser beams in movies, but they aren’t, they are almost all IR, and a few are sonar.
The following thread is a detailed discussion. Of course specific devices and any Groovy code will be out of date, but the basic idea still applies, and some of the brands, like Dakota, are certainly still available. Then you connect that to something that can communicate with smartthings, typically a dry contact device.
Here’s discussion of a version that’s still available:
Looking to Connect IR Beam Sensor to Flood Lights - #4 by krlaframboise