3 light in back seet ceiling?

Those are censors to detect if there is any movement in the back seat. This is a safety thing. If you leave a baby or a pet in the car, the Tucson will tell you to check the back seat. Also, if you neglect to check the back seat the Tucson will notify you via blue link on your smart phone. Also the alarm will sound and the lights will flash

I noticed as part of the trim levels and options packages that the so-named 'rear seat alert' even in the base model apparently gets an upgrade to something called, 'ultrasonic rear seat occupant' included in the Convenience Package. I'm not planning on getting in the weeds on the difference in the two descriptions or designs as I've not gotten delivery yet. All I can imagine is the base just uses a weight sensor in the seats the same as real old design 1st gen seat belt warning buzzers used to.