Millions of American kids come home to or leave an empty house every day. However, parents are increasingly using an existing technology -- home security   systems -- to keep an eye on their "home-alone" children. In the early days of home security, the systems were basically designed just to keep the bad guys out. Now, many parents are also using them to make their children safe when they are at home alone. Below are some simple rules for adults to teach their children: Every child should memorize his or her own full name and address, and home, work and cellphone numbers of each parent. Also keep this information posted next to the phone at home. If your child is too young to memorize the information, he or she may be too young to be home alone -- for any time. Teach your child to observe things around him or her when he or she returns to the house. If a door or window is slightly open, the child has any reason to suspect   someone has been in the house that shouldn't be, have him or her call you, then wait at a safe house a neighbor offers. Warn your child never to answer the doorbell or telephone when they are home alone. Besides, set a rule that he or she must never play outside the house when no one else is at home. Be sure he or she knows how to disarm   and arm your home security system. Program your control panel   to give you a message when your child enters or leaves the house, and arms or disarms the system. If your child forgets to rearm the system, you can call him or her with a personal reminder. To learn more about home security systems that can help parents protect their "home-alone" children, visit www.ProtectAmerica.com. According to the passage, home security systems   _  .
can help children all the time are now used for protecting the children were first designed to keep kids safe at home are developed to spare parents more time for their work