The processing power to identify human-like temperature variations would be difficult and probably unreliable. It would need to identify a full-size adult and a newborn baby, also dogs, cats, etc. to be a really good system. I'm not saying it's impossible, I think it's actually a very good idea, but it is difficult.
There are other mechanisms that can be used. For instance sonic motion detectors could maybe be used, they tend to be very sensitive. I'm not sure how well they'd work just for the inside of a car, but also a sleeping baby may not make any motion for sometime....so that wouldn't be the end of it either.
Similar to alarm technology, I would suggest an array of sensors with intelligent filtering built in to the system. For instance, if the thermal sensor triggers the system, it should enter into the checking phase. Then if one of the other sensors triggers, such as the motion sensor (that is somehow fixed just on the iside of the car), then the system should enter into a heightened state of alert, or a warning state. Then if one of the other sensors thinks it has detected something then maybe the alarm safety system should activate and trigger the alarm.
Other sensors to consider:
Seat occupancy sensors. Some cars already come with them to notify you of seatbelts or to automatically disable front airbags if the weight is too low.
Child seat occupancy sensors that use a standard system for communicating with heat sensor alarms, so if there is an occupied child seat in the vehicle the alarm system will be aware of it and remain in a heightened state of alert.
Audio sensors. Listen for sounds made by children or human voice that is at such a level it must be from inside the vehicle.
One must keep anti-theft in mind, though.
Uhhhhh....hope I didn't just do your project for you. Anyhow, sounds like it's already under consideration, but will the prof know that?
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