Use a pressure mat. These are quite easy to integrate to smartthings, you can find one graded to a light enough weight, and unless you have someone using a cane in the home it should be possible to set it up so that it is not a tripping hazard. And you don’t need to attach anything to the vacuum.
In the past people have use these for a welcome mat, for Halloween decoration theft detection, and on beds and sofas to tell when someone is occupying them, but it should work for your use case as well. 
You will need to decide whether you also want the lights to come on when a person steps on the mat or whether you want to only have the mat trigger the lights when the home is in “away“ mode. Just depends on the details of your use case.
You could also set up a trip beam but those require a lot of technical knowledge and quite a bit of work, so I don’t usually recommend that.