This tip came from a neighborhood watch coordinator.
Put your car keys beside your bed at night. If you hear a noise outside your home or someone trying to get in your house, 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.
Next time you come home for the night and you start to put your keys away, think of this: It's a security alarm system that you probably already have and requires no installation. 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 key fob chain. It works if you park in your driveway or garage.
If your car alarm goes off when someone is trying to break in your house, odds are the intruder won't stick around.... After a few seconds all the neighbors will be looking out their windows to see who is out there and sure enough the criminal won't want that.
And, remember to carry your keys while walking to your car in a parking lot. The alarm can work the same way there..... This is something that should really be shared with everyone. Maybe it could save a life or a sexual abuse crime.
It would also be useful for other emergencies, such as a heart attack, when you can't reach a phone.