This article lists ieight of them:
8 Life-Saving Car Seat Alarms That Remind Parents Theres a Baby in the Back Seat
https://www.fatherly.com/gear/best-car-seat-alarms/
Nissan now provides a car alarm for this purpose:
Nissan's rear-seat alert meant to help deter child heat-related deaths
By Doug Phillips | South Florida Sun Sentinel |
Aug 01, 2018 | 5:25 AM
Nissan is making its Rear Door Alert technology standard on all of the companys 4-door vehicles beginning with the 2019 model year to help reduce heatstroke incidents, the manufacturer announced Tuesday.
The technology was introduced as standard equipment for the Pathfinder SUV for 2018 and is now being expanded to another eight models, including the popular Rogue and Altima designs.
Heres how the Rear Door Alert works: The vehicles operating system notes when a back door is opened at the beginning of a trip. If so, the horn will honk at the end of the trip to remind the driver to check the back seat. The feature can be turned on or off using the vehicles on-board computer menu.
In 2017 there were 43 deaths across the U.S. of children from heatstroke inside vehicles, according to the the group KidsandCars.org. So far in 2018 there have been 29, including a 17-month-old boys July death in Pembroke Pines and the February death of a 1-year-old boy in Miami.
More:
https://www.sun-sentinel.com/business/fl-bz-nissan-rear-seat-alert-20180801-story.html
All car companies could do that, though as noted in the first article, an effort to pass a requirement failed in the US Congress.