Alarms and Detectors: Finding the Right One for Your House
Home Intrusion Alarm
Wide variety of types available. Selection will depend on what the customer wishes to accomplish. Some feel a loud alarm at the point of entry will scare away the intruder. Others prefer a remote alarm located in a bedroom that will alert only the homeowner. Others prefer an outside alarm that will alert neighbors. Other kinds will sound an alarm and are connected directly to monitoring systems that will alert the police.
Simple alarms may consist of a door-locking device with a buzzer attached. When the device is tampered with or the door opened, the alarm sounds.
Many intrusion alarms are more elaborate and have twocomponents. A perimeter alarm detects intrusion at points of entry, such as door and windows. An area alarm detects motion inside a room.
Some types use low-voltage wire, similar to stereo speaker wire, to connect magnetic window and door sensors to a control panel.
Other types use radio transmitters at each door and window sensors to trigger an alarm at the control panel.
Alarm sounds when the window or door opens.
Alarm systems designed for d-i-y installation are frequently battery powered, so ease in testing the batteries can be an important feature. Some systems sound a warning when the batteries are low.
Hard-wired systems may have a button on the control panel that checks the entire system.
Uses either ultrasonic waves or microwaves to detect motion. When it detects motion, it triggers an alarm.
Generally plugs into a standard electrical outlet, so they’re easy to install.
Ultrasonic detector waves only go as far as the wall of the room, while microwaves penetrate walls and windows.
Some ultrasonic alarms use a narrow sonic beam that must be bounced off a hard surface. Here, the intruder must break the beam to be detected.
Other ultrasonic alarms use a wide beam that fills the room and detects motion anywhere in the trap zone.
The most important consideration with this type of alarm is avoiding false alarms. These can be caused by air conditioners or drapery moving above a hot air register. Better systems have built in circuitry that does not respond to these types of signals.
Some systems have extra repeater alarms or satellites. These can be plugged in anywhere in the home to add extra noise and relay the warning to remote rooms.
Measures the changes in electric current caused by invisible particles ionized in the heat of combustion.
Transforms air inside the detector into a conductor of electric current. When smoke enters the detector and impedes the flow of current, the alarm sounds.
Responds particularly well to the smoke caused by a flaming fire.
Requires little power and is effectively powered by household batteries.
Slower to respond to a smoldering fire.
Detectors are required to emit a low warning when batteries are weak.
Uses a small lamp adjusted to direct a narrow light beam across the detection chamber. Smoke entering the chamber scatters this light beam, causing it to hit a sensor and set off the alarm.
Usually more sensitive to smoke from a slow, smoldering fire than an ionization detector, but reacts less quickly to flaming fires.
Available in both battery-operated and plug-in versions.
Used primarily by large commercial firms
The alarm sounds when the temperature rises to a certain level.
Most are also triggered by a quick rise in temperature even if an extreme temperature is not reached.
Not as safe as other types of fire detectors as fire usually must be intense before the thermal unit will sound.
Detects carbon monoxide, a colorless, odorless, deadly gas that poses a potentially deadly health risk to people.
Measures the amount of carbon monoxide over time and sounds an alarm before people would experience symptoms.
Operates on batteries or can be plugged in.
Some models provide a running digital readout of CO levels.
Hard-wired or plug-in models typically use some type of solid-state sensor, which purges itself and resamples the air periodically. That cycle increases the power demand.
Battery-powered detectors typically use a passive sensor. They will operate even in case of a power failure.
Available in combination units that have CO and smoke detectors in the same unit.
Detects radon, a colorless, odorless, radioactive gas formed wherever there is uranium, an element present throughout the crust of the earth. It poses little risk if it makes its way to open air, but if it seeps into a house, it can collect in hazardous concentrations.
This detector consists of a small sheet of plastic. Alpha particles that strike the plastic cause microscopic pockmarks.
After an exposure period, users mail the detector to a lab. The lab’s count of the pockmarks gives a direct measure of the mean radon concentration.
Another type uses activated-charcoal granules, which trap radon gas. After an exposure time, the container is resealed and shipped back to a lab for analysis.
Plugs into a standard outlet.
Samples air continuously for radon and provides updated reading on the display.
Alarm sounds when the long-term average of radon level passes an acceptable level.
Alarm will be repeated until the radon level drops back to the accepted level.
Home Perimeter Alarm
Home Area Alarm
Ionization Fire Detector
Photoelectric Fire Detector
Thermal Fire Detector
Carbon Monoxide Detector
Alpha-Track Radon Detector
Continuous Monitor Radon Detector