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A Field Guide to Household Technology

Chicago Review Press Incorporated

ENTERING THE HOME

HOW DO YOU KEEP unwanted people out of your house while letting the family in? This problem is as old as buildings; once people put up walls to keep out intruders, they had to have doors to control egress, and systems to secure the doors.

In modern homes we use a variety of devices. Some, like locks, have roots in the ancient world and others are newcomers. With the miniaturization of electronics and development of new sensors, entering the home has gotten a lot more technical than it was even a few years ago.

Door Chimes

BEHAVIOR

Alerts you to visits from Aunt Kay, the UPS driver, and Girl Scouts selling cookies.

HABITAT

The button that activates the chime is mounted on the outside doorway of the front door. The chimes themselves reside indoors, usually high on a wall adjacent to the doorway.

HOW IT WORKS

Doorbells and chimes rely on electromagnets to operate. When Aunt Kay pushes the doorbell button, she completes an electric circuit that sends current through a transformer (to change the voltage) to an electromagnet inside the bell or chime box. The electromagnet becomes magnetized when current flows through it, and the now-energized magnet pulls a metal arm that strikes the bell or chime. When the current is interrupted, the electromagnet loses its power and a spring pulls the arm back.

In chimes, the electromagnet is part of a solenoid, or simple electric motor. A solenoid moves back and forth, unlike most motors, which move circularly. With the button depressed, the solenoid moves forward striking a chime (metal bar) that plays a note. When the button is released, the solenoid is pulled back by a spring so it hits a second chime on the opposite side. Together the two chimes give the "ding dong" sound.

On buzzers and bells, the electromagnet propels an arm to strike the metal bell. As the arm moves, it interrupts the electric circuit. With the circuit now open, the only force on the arm is a spring that pulls it back to its starting position. Now back at its initial position, the arm makes electrical contact again, re-energizing the electromagnet, which pulls the arm to strike the bell, over and over again.

Storm Door Closer

BEHAVIOR

It pulls the storm door closed, but allows it to close gradually.

HABITAT

Attached to the inside of storm doors. One end is screwed into the door and the other is screwed into the door frame.

HOW IT WORKS

Before this type of closer was used, long springs pulled screen doors closed. This tended to slam the door shut, which often caused it to rebound open and slam shut again. And again.

To prevent this "slam-slam" annoyance, and to prevent damage to the glass in a storm door, pneumatic closers are often installed. Inside the metal tube is the spring that pulls the door shut. A piston is inside. As the door is opened, the piston extends and draws air into the tube through an opening. Releasing the door allows the spring to pull it shut, but the piston is now pushing air out of the tube through a small hole that resists this motion. The air opening has an adjustable valve so you can control how quickly the door closes.

The closer also has a stopper so you can prop the door open. This is very handy when you're hauling in bags of groceries. The metal stopper slides on the piston shaft. Setting it at an angle wedges it into the shaft to hold the door.

A safety chain and spring prevents the door from opening so far that the closer or the door hinges get damaged.

Front Door Lock

BEHAVIOR

Keeps out (some of) the people you don't want inside, but gives those you do want inside easy access.

HABITAT

Mounted on the side of the door opposite to the hinged side. Located at a convenient height to allow users to insert a key to open the door.

HOW IT WORKS

Most doors use a cylinder lock. Inserting the correct key allows you to rotate the cylinder, which is connected to an arm that withdraws the latch keeping the door secure. The latch is usually pushed closed with an internal spring.

The beauty of the lock is that each has its own code that protects it. The code is cut into a metal key. The vertical indentations in the key correspond to both the placement and heights of pins inside the lock. As the key enters, it pushes the spring-mounted pins up and out of the way. A key with the incorrect code will not push the pins to the height that allows the cylinder to turn.

From inside the house you can operate most locks by turning a knob. This is a nice safety feature so you don't have to find a key to escape a fire. On the other hand, for higher security from intruders, some locks require keys on both the inside and outside to open. The inside key prevents someone from breaking an adjacent window and reaching through it to open the door. It can also prevent people-toddlers or burglars who entered another way — from exiting the door.

Security Door Viewer or Peephole

BEHAVIOR

Gives you a wide-angle view of your front porch area from behind the front door.

HABITAT

Found at eye level, or a bit lower to accommodate shorter people, in the middle of the front door.

HOW IT WORKS

The optics in the peephole work like a wide-angle lens. The glass refracts or bends light to collect images from a wide swath and focus them into the small viewing port. Some peepholes have large viewers so you can see outside from several feet back from the door. Other peepholes even allow you to connect a video camera.

Standing outside and peering in, you can't see much at all. Of course, some creative people make a viewer (for law enforcement agencies) that fits on top of the outside of a peephole and allows them to see inside.

Keypad for Home Security System

BEHAVIOR

Allows the owner to enter a code to arm and disarm the security system.

HABITAT

The keypad is located inside the house, near the entry door used most often. It is inside to protect it from tampering. Being inside requires that it have a programmed delay (about 30 to 45 seconds) so the owner can enter the house, turn on a light, and disarm the system by punching in a code before it triggers an alarm.

HOW IT WORKS

A microprocessor inside the keypad allows you to set and change the code. It also allows you to turn on parts of the system rather than energizing the entire system. For example, if you were alone inside the house, you could activate the perimeter alarm (to alert you that someone had entered the house), but not the motion detectors. This would provide security without your movements inside the house setting off the alarm. Or you could activate the alarms in one part of the house but not the entire house.

Although the typical five-digit code used in many alarms would be easy to crack, intruders only have a few seconds to enter, find the keypad, and try a few codes before the alarm sounds.

The keypad can activate local alarms or send alarms to off-site security companies or even police departments. Some systems integrate entry alarms with fire alarms.

Perimeter Entry Detector or Burglar Alarm

BEHAVIOR

It alerts you or a security company that someone has entered the house through a door or window.

HABITAT

On homes with this type of security system, look for detectors with wire leads on door-sills and alongside windows.

HOW IT WORKS

There are several types of perimeter alarm detector, but most common is one that uses magnetic reed switches. A magnet is attached to a door or window. When the door or window is closed, this magnet lies adjacent to a magnetic switch attached to the doorframe or window frame. With the alarm armed, if someone opens the door or window, he moves the magnet, which was holding the switch in the closed position. Now free of the magnet's pull, the switch opens and causes the alarm to sound.

Perimeter alarms make it difficult for an unwanted visitor to gain access to your home. If a visitor does gain entry, security systems have a second level of alarms that detect motion within a room.

INTERESTING FACTS

Stores use perimeter entry detectors to let the clerks know that someone has entered the store. These typically use visible or infrared beams of light that cross the entry of the store, just below knee height. When you enter, you interrupt the beam of light and that causes a "gong" or bell sound. Usually these devices are clearly visible, mounted on each side of the door.

Perimeter Alarm Switch for Doors

BEHAVIOR

Sends a signal whenever the door has opened.

HABITAT

Built into the door frame, where it is very difficult for burglars to find and disconnect it.

HOW IT WORKS

This is a simple spring-loaded on/off button that is installed into the doorframe. When closed, the door holds the button in its compressed position. When the door opens, the internal spring pushes the button out signaling that the door is open. With the alarm turned off or with that zone of the alarm system turned off, opening the door doesn't trigger an alarm.

INTERESTING FACTS

This simple electrical system is unlikely to fail. Since intruders can't see the alarm switch from outside (or from inside for that matter, unless the door is open), they can't disarm it.

Motion Detector

BEHAVIOR

It senses your cat wandering around the house at night or, possibly, that burglar you've always feared.

HABITAT

You can spot these devices hanging high on a wall, often in the corner of a room. They are usually the same (approximate) color as the wall so they blend in. They have what appears to be a curved lens, and some have an active LED (light emitting diode) to indicate that the sensor is working.

HOW IT WORKS

Most motion detectors use infrared imaging. All objects emit infrared radiation; the sensor detects major changes in the amount of infrared radiation in the room. It sends an alarm when it detects a significant change in the infrared energy. Someone entering an empty room will add infrared radiation that the detector can distinguish.

The combination of perimeter and motion detectors makes it quite difficult for anyone to enter undetected. Unless someone wants to go to the lengths of Mission: Impossible to get in, it's easier to find a less well-protected home.

Video Monitoring Camera

BEHAVIOR

Allows occupants to see who is at the front door from any television set in the house.

HABITAT

Found at gated developments and at front porches. It is positioned to give the best view of anyone standing at the door.

HOW IT WORKS

The video camera sends its signal to a modulator that is probably mounted on a wall in the utility room, basement, or closet. The modulator converts the signal to a television UHF (ultra-high frequency) channel that the user selects.

When someone rings the doorbell, the user changes the television channel to the selected UHF channel to view the video coming from the front porch. If the user has an intercom system, he or she can talk to the magazine seller waiting to give the pitch, and can send the seller away without coming to the front door.

Garage Door Opener

BEHAVIOR

Lets you open the garage door without getting out of your warm, dry car and walking through the cold, drenching rain.

HABITAT

This remote control is found on the visors, dashboards, and glove compartments of many cars. The receiver and motor are mounted from the ceiling of the garage.

HOW IT WORKS

Unlike the TV remote control, the garage door opener uses radio waves, not light. Older systems use tiny switches to encode a signal into the transmitter (in the car) and receiver (adjacent to the motor that opens the door). By encoding the signal, your neighbor (hopefully) will not open your garage door when trying to open his.

Newer systems have much more elaborate electronic systems for encoding the signals to prevent burglars from capturing the signal and entering your house. Transmitters and receivers generate new codes each time they function, thus making it very difficult for someone to swipe a code.

For more information on the garage door opener itself, see page 142.

BEHAVIOR

Allows you to open your garage door without the handheld remote control unit kept in your car. Coming back from a bike ride or otherwise locked out of your house without a front door key, you can enter your personal code to open the garage door.

HABITAT

Mounted on the doorframe of the garage door or on an outside wall.

HOW IT WORKS

Punching in the code (which you can usually set yourself) that is recognized by the logic circuit in the garage door electronics opens the door. The opener is wired to the electronics, which are housed adjacent to the motor near the ceiling and near a power outlet.

Keyless Entry Device

BEHAVIOR

Allows you to lock and unlock your car doors and trunk without a key. Also allows you to find your car in a crowded parking lot when you've forgotten where you've parked it. This is an especially valuable function when renting a car.

HABITAT

Found amid pocket lint in the pockets of many Americans. Usually found on a key chain or ring with a set of traditional keys, just in case the battery inside the remote entry device should die.

HOW IT WORKS

A computer inside your car monitors the several different kinds of signals that you might send to unlock the doors. You could enter a code on the outside of the driver's door, push a button on the inside of either front door, or push a button on your keyless entry device or fob.

When the car computer detects the radio signal from your fob and determines that it is the right signal (and not the guy parked next to you trying to get into his Lotus), it powers a motor or actuator. The actuator, which has a small DC motor and gears inside, only moves up or down. Moved up, the actuator pushes a lever that connects the outside door handle to the lock, allowing you to open the door. When you push "Lock," the actuator moves down and disengages the outside door handle from the lock. No matter how hard you pull on the handle, it won't open the door.

Intercom

BEHAVIOR

Allows you to play a radio station on speakers throughout the house and to talk to other people throughout the house or at the front door.

HABITAT

Usually there is a speaker outside the front door and in several rooms. A control box with a radio built-in is usually located in the kitchen or a central hallway or entryway.

HOW IT WORKS

Older home intercoms had units throughout the house wired to a master unit. Newer systems are wireless.

Wireless units (not requiring installation of wires) either operate as broadcast radios or send signals through your existing electric wires.

Some intercoms come with video screens, so you can see the person standing at the front door selling magazine subscriptions.

LIVING ROOM, FAMILY ROOM, AND DEN

ENTERTAINMENT SYSTEMS DOMINATE the technology of these living spaces, and entertainment systems typically run on electrical power. So, much of the technology found here is found plugged into electric wall outlets.

Of course, not everything in these rooms is related to entertainment. No one would consider a vacuum cleaner a source of amusement.

Vacuum Cleaner

BEHAVIOR

Sits quietly until company is about to arrive. Then it roars to life, lifting and sucking dust bunnies and dirt from carpets and hardwood floors.

HABITAT

When not in use, stored in a hall closet. In the hands of a frantic cleaner, it can be used almost anywhere in the house.

HOW IT WORKS

Vacuum cleaners are marvels of engineering. A motor drives a fan that pulls dirt-laden air inside. It pushes the air into a porous collecting bag that traps the dirt. When full, the bag is removed, thrown away, and replaced with a new one.

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Excerpted from A Field Guide to Household Technology by Ed Sobey. Copyright © 2006 Ed Sobey. Excerpted by permission of Chicago Review Press Incorporated.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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