KPG

How would I open the door of my S5, to open the hood and get a jump?

Aarononymous

With the key blade/seperate the main keys or isn't there a half to the spare key as well?

AofC_RR

Yep exactly right

local3

Yes, the key to open the door lock separates from the keyfob (press button on it), also, if the battery on your keyfob should fail and you want to start the car, you need to have the "wallet key" (black plastic key that came with your car) which you insert into the keyfob adapter in your glove box and then you can use this adapter+wallet key combo to start the car by inserting it to the keyfob hole.

The wallet key can of course also be used to open the driver's door lock.