If your S70 has the factory alarm installed, there is a microswitch fitted to the hood latch ditectly forward of the battery. Wire colors are yellow-black (yellow with a black stripe or black with a yellow stripe) and black.
If you have an aftermarket or dealer-installed alarm, this might have been a hood switch added later.
A third possibility is that the factory hood latch switch failed, so someone replaced it with a less-expensive substitute.