The next time you come home for the night and you start to put your keys away, think about this: The panic button on the car remote is a security alarm system that you probably don't realize you already have and requires no installation. Put your car keys beside your bed at night. If you hear a noise outside your home or someone trying to get into your home, just press the panic button for your car. The alarm will be set off, and the horn will continue to sound until either you turn it off or the car battery dies.
Test it. It will go off from most everywhere inside your house and will keep honking until your battery runs down or until you reset it with the button on the remote. It works if you park in your driveway or garage.
If your car alarm goes off when someone is trying to break into your home, odds are the person won't stay around .... after a few seconds, neighbors should be looking out their windows to see who is out there. A criminal won't want that attention.
Also, remember to carry your keys while walking to your car in a parking lot. The alarm can work the same way there.