A shop owner is shutting up shop for the night. Before leaving, the owner sets the security alarm by punching a code into a keypad.
Many people use security systems to stay safe. Security systems use signals that tell them when to sound the alarm. Codes are entered in a keypad near the door. This turns the system on and off. If you forget to turn off the alarm when you return, the alarm will sound.
Many security systems use a motion alarm. A small transmitter inside the house sends radar waves into the room. The waves scatter and bounce around the room. They set up an invisible pattern. When someone enters the room, the pattern is upset, and the alarm goes off. A motion alarm will not work well if you have pets. When the pets move, they set off the alarm.
Another type of security system uses metal strips on the windows. When the window is closed, the metal strips touch each other. When the window is opened, this connection is broken and an alarm goes off.
Security signals keep us safe in many ways. Airports and courthouses use metal detectors to detect weapons. Many look like doorways. A transmitter on each side of the doorway sends out radio waves. Metal absorbs some of these waves and reflects them, or sends them back. The detector’s transmitter then beeps, or signals that metal is there.
Libraries and stores prevent theft by placing coded targets on items. The target sets off an alarm at the exit if it has not gone through the check-out process.
Picture Credit : Google
