Keep it on your nightstand
If you have a newer car, it probably came with a key fob with a panic button. It's more useful than just setting off your car alarm by accident every now and then – it's handy for personal safety inside the home. Not only can it be used to alert someone around your car who's up to no good in the parking lot, keeping it by your nightstand while you're home has a safety benefit as good as a barking dog (another layer of protection).
It's 2am and you're awakened by a sound near one of your first floor front windows. You get up to see what it is (with your tactical flashlight, of course) from your bedroom window and notice someone trying to find an opening to your home. You hit the panic button to your car alarm (from the key fob on your nightstand) and flash him with 1,000 lumens of blinding light, scaring off the trespasser.
The point? Simple. In the event that someone is lurching around your home (among other safety measures), the sound emitting from your screeching car alarm (if close enough to the incident) will be loud enough to draw attention he doesn't want – not to mention 1000 lumens directly into his thieving face will impair his vision. It's usually enough to scare off would-be burglar. (If not, well... execute plan B.)
Don't have a key fob? Many home security systems come standard with them (or offer a separate panic button option) that you can keep in a few rooms. Either way, keep one by your nightstand as a layer of deterrence used with other tools and tactics for protection.