Hi,

As far as i know.

1 To check upto what distance the alarm will detect 
2.To whether it alaram will detect if some use uses a smoke 
or fire inside the car
3. To check if some one puts fire / smoke apart from front 
and rear (i.e. if some one comes up with fire from other 
remaining side of car)
4.To check for what kind of smoke the alarm detects(i.e. 
when the car is moving and stops at signal and in front of 
this car if some other car ejects smoke will this alarm 
detects then it will be a problem ( I think this you need 
to ask to the interviewer what kind of smoke it detects 
whether it detects all kinds of smoke or smoke only from 
plastic covers etc.)

HI Mr,
Use Decision table testing technique.

Cheers
sridhar