Many schools, businesses, and homes have security systems that use lasers. A basic system would have a laser on one wall beaming at a sensor on another wall. The alarm won’t go off as long as the laser continues to hit the sensor on the opposite wall. But if someone walks into the room and disrupts the laser, then for a brief moment the laser won’t hit the sensor and—you better get moving—the alarm’s going off! Typically, the lasers used in these types of security systems can’t be seen with the naked eye—that would make it pretty easy for burglars to get around them. Instead, they might use infrared lasers, which look invisible to you and me. In the movie that Ada saw, the actors used mirrors to bounce the laser beam around them so that it would still hit the sensor while they walked into the room. In reality, this would be pretty hard to pull off. But, hey, that’s movie magic!