It's EXTREMELY dangerous to leave a dog shut in a car in the summer. But sometimes you need to stop for groceries or something and you've got the dog with you and can't take him (or her) into the store.
You've had the air conditioning on, and the car is reasonably cool. So you leave the windows
open, and the sunroof, and scuttle in. But if you get distracted (maybe the sales assistant is exceptionally stupid) you may not realise how much time has elapsed.
Have a thermometer in the car with a radio transmitter. Have a receiver in the keyfob you use for the central locking/alarm/. When the temperature in the car reaches a dangerous level (30 Centigrade ?), the alarm goes off and you get a PeepPeepPeep to remind you to go and check on the doggie .....
These things should be compulsory. 5 minutes after the beeper goes off, the car itself starts to squauk, and the doors automatically unlock so that bystanders can open it up and let the dog out. If they steal your stuff and your car, good. You deserve it, you b@st@rd.