You can also just thunk your hood with your hand a couple times; if you have neighbors, they will appreciate not hearing a car horn every morningAddition to 13 (two pages ago)
If you can, honk your horn before you turn it on.
I once acutally had to pop my hood because a cat (chased by my dog) went into the engine from underneath and when I popped the hood, was sitting on top of the engine. Figure that one out, lol. I wouldn't have even seen her if I hadn't seen the dog chase her into my truck.
Honking the horn will usually scare what ever is in your vehicle that you cant see, out of it.
Also do this for riding lawn mowers and any other motor vehicle (like a ATV) that has an enclosed engine.