ROANOKE TIMES
Copyright (c) 1995, Roanoke Times
DATE: Tuesday, December 19, 1995 TAG: 9512190020
SECTION: EXTRA PAGE: 6 EDITION: METRO
COLUMN: At Home With Technology
SOURCE: DAVID BUTLER
Q: Since I work out of my home, I receive business mail on a daily basis. Unfortunately, I can't see my mailbox from the house. Is a small radio device available that would inform me when the mail arrives? Also, I'd like to be alerted when someone pulls into my driveway.
A: The easiest way to receive notice when your mail arrives is to install a wireless shock sensor in your mailbox. Shock sensors are commonly used by security professionals to protect gates, fences and windows. A wireless shock sensor includes a built-in radio transmitter, eliminating the need for buried wires.
The sensor unit simply attaches to the inside of your mailbox door. It's basically a mercury switch (similar to that found in mechanical thermostats) connected to a battery-powered transmitter. Models available from two companies have maximum ranges of 200 and 300 feet, respectively.
When the carrier opens your mailbox, the indoor unit (``receiver") notifies you with a short beeping sound. In case you miss the beep, an LED remains lit until you press a reset button. The unit will also alert you if vandals try to smash your mailbox. Who knows? You may actually catch one in the act!
If your mailbox is beyond the reach of a conventional transmitter, you might consider building your own alert system using a car alarm pager (range: up to two miles). For power, a rechargeable sealed lead-acid battery is best, though summertime heat will definitely reduce battery life. Although postal regulations don't prohibit mail box alerts, you may want to check with your local postmaster.
Driveway alerts work much the same way as mailbox alerts except that they use a motion detector instead of a shock sensor. Depending on the model and the local terrain, you can expect a range of 75 to 200 feet. Again, the indoor units provide both audible and visual indications.
Keep in mind that motion detectors are prone to interference. Leaves and critters are the usual culprits. However, since the desired target, a motor vehicle, is relatively large, you can virtually eliminate false triggers. By mounting the detector close to the driveway, you can lower the sensitivity until it only detects large, nearby objects such as an automobile.
If you have access to a trenching machine or don't mind doing some digging, a hardwired magnetic probe is the most reliable method for detecting vehicles. Magnetic probes are routinely buried in city streets to sequence traffic lights. Unless you have a gravel drive, you need not bury the probe directly in the vehicle's path. Magnetic probes work equally well when buried alongside the drive.
Only special cable designed for ground contact should be used to connect a magnetic probe. Most manufacturers ship probes with cable already attached. Because the electrical field induced by passing vehicles is very small, an on-site splice could render the probe useless. Standard cable length is usually 100 feet, although most companies will supply longer cables on request.
The indoor units that come with magnetic probes usually have external connections. If you want to monitor the driveway from your security panel or home control system, be sure to choose a model with an auxiliary output relay. The relay could also be used to trigger a special power line carrier (PLC) module which, in turn, could sound a remote chime module or turn on a lamp.
To receive a list of companies that manufacture mailbox and driveway alerts, please send $1.50 and a self-addressed envelope to David Butler F-543, Department TWN, 14713 Pleasant Hill Road, Charlotte, N.C. 28278-7927. The list includes toll-free phone numbers and a summary of each company's products. You'll also receive a parts lists for a do-it-yourself long-range alert system.
HomeTech News: In January, three new home automation publications will debut. Custom Home Electronics and Home Systems Installer are trade "rags," while Popular Home Automation hopes to win favor among hobbyists and do-it-yourselfers. For details on these and other resources, write to me at the above address for a copy of my Home Automation Resource List (F-539). Please include $1.50 for postage and handling.
LENGTH: Medium: 79 lines ILLUSTRATION: GRAPHIC: Buried probe beside the driveway warns ofby CNBapproaching vehicles. Wireless shock sensor triggers an alert when
mail arrives.