Under-mat pressure sensors, and laser beams at waist height are generally good indicators of a solid body moving at a specific place at that time. Under driveway magnetic sensors can ascertain the presence of a vehicle. Sometimes a pet gets latched in the workshop or garage. If you see the sensor going off, and you know the door's closed, you know you might just have a trapped pet. If however, that sensor goes off, and you know that it is not reasonable, then it is likely there's an suspicious body in that area.
Good fences make good neighbors.
A good security system keeps neighbors good. XTension and your Macintosh make it fun.