The upside of good strong locks are that they are good deterrents to people trying to get into your home. You may already have some on your doors and windows. Of course, if someone really wants to get in and they can see you don' t have an alarm company service they may be still motivated to find a way. What will stop them or at least give you the obvious warning that someone is there so you can call police (or perhaps even prompt a neighbor to do so when they hear it), is the piercing, screeching sound that is emitted the moment they go to open the latch to come inside. Features 95db alarm and a 45second reset time. Battery included.
