About Wireless Home Alarms

Wireless door alarms are often based on a "closed circuit" system, which means that electricity is flowing through it constantly. When the door or window is opened, the flow of electricity stops and an alarm goes off. This is achieved through a two-part system. The first part typically consists of a magnetic strip screwed into the door of the window itself. The second part is the trigger and alarm system, which is screwed into the door or window frame and lines up with the magnet. The magnet holds a spring or a switch in place on the trigger mechanism: when the magnet moves, the spring or switch cuts off the electrical flow from the battery.

Motion detectors are often very small these days, and can cover an entire room or yard area with little effort. (Modified versions are used in most shops and grocery stores these days: they automatically open the door when you approach.) They utilize microwave signals which bounce off of objects in the area and return to the sensor. When someone steps into the area, those signals bounce off of the person and come back to the sensor faster (i.e., at a different frequency). That's enough to activate the switch and throw the alarm.

Passive infrared (or PIR) motion detectors operate on similar principles to microwave motion detectors. Instead of bouncing radar signals off of objects in the area, they monitor the ambient heat and the infrared energy which it entails. When a warm body of sufficient size moves into the area, the amount of IR energy spikes, which is enough to activate the alarm.

Light beams are very simple wireless alarms which work best on stairways or halls. A beam emitter is placed on one side which projects an invisible laser light across the passage. A trigger mechanism catches the beam on the other side. As long as the beam is unbroken, the current keeps flowing and the alarm stays silent. When someone breaks the beam, the current is shut off and the buzzer activates. Light beams work best when they are placed at about waist height, which allows pets to pass under them without triggering a false alarm.

All types of wireless alarm are designed to be portable, with a fully-self contained mechanism that runs on household batteries such as D-cells or 9V. They can be installed using simple screwdrivers or drywall anchors, and turned on and off with just the flick of a switch. Most electronics stores sell them very inexpensively, allowing an entire house to be fitted for comparatively little cost. The downside is that they simply emit a loud noise, which can wake the household and hopefully send burglars packing, but do not call the police or emergency services. (Some of the most sophisticated modules can be plugged into the phone jack and play a prerecorded message for 911, but most do not.) That means the homeowner should develop a plan for reacting to a wireless home alarm, and be prepared to take additional steps when it goes off. Make sure everyone in the household knows what to do in the event of a break in and have a central gathering place outside the house where everyone should go. Tell your neighbors about the wireless alarms and ask them to call the police if they hear it go off when you aren't home. Finally, because they run on batteries, wireless alarms should be checked regularly: replace their power source at intervals dictated on their packaging (usually every six months or so).