as the post says elxiah the basic parts would be:
1) Sensors (which will indicate danger)
2) circuit (it will link the sensors)
3) Alarm system, as for this i was thinking of a small headphone in one of your ears, which could make a little sound when the sensors catches something.
4) Power plant, well this is obviously for all the parts (micro-controller, sensor, some kind of alarm).
So i think those are the simple parts as for the quantity of the sensors they should be strategically put on the suit for all directions (back, legs, head, both right and left ribs).