Specifically, Tesla wants to use a currently unlicensed sensor that would better provide a more accurate look at passengers or items left in the car. The issue is the sensors run at higher power levels than currently permitted, hence the FCC filing.
But the technology itself is far more advanced than weight sensors embedded in a seat or camera-based technology. Tesla's solution is actually a motion-sensing device, which provides depth perception and the ability to see through some materials like a blanket on top of a child, for example. This sensor is also more intelligent and can identify objects better. Current rear-seat reminders will ding for anything left behind, but this potential enhancement could reduce "the likelihood of false alarms" when it comes to a child.
Tesla also mentioned a couple of other benefits when it comes to this sensor. It could enhance antitheft systems and provide more accurate seat belt reminders, too. And compared to a weight sensor, the motion sensor could "optimize airbag deployment in a crash," based on whether a child or an adult is seated. Surely, this sensor would beef up, too.