How many times have you been at home and with no warning you get a knock on the front door. Rapidly you pull yourself together to get to the door before they leave. It would be so much better to have an alert sound when a vehicle enters your driveway or a visitor walks up your sidewalk.

Driveway and entry annunciators have been around for many years. To add them to your home automation and security system can add a whole new meaning to convenience. They can provide you not only with being alerted when a visitor approaches, but also turn on lights for safety and convenience.

There are two primary technologies used to sense vehicles driving up a driveway:

Magnetometer ? A magnetometer senses metallic objects as they pass the sensor. Since an automobile is made of metal, it is easy to sense as it passes a magnetometer sensor. The sensor is encased in a waterproof plastic housing, 12 to 18 inches long. The majority of magnetometer sensors are buried along side the driveway at 6 to 8 inches deep. A cable connects the sensor to a receiver control box in the house, or some systems are available that are battery powered and can transmit a radio signal to a receiver in the house. With a wired system, the cable is normally buried in the ground leading to the house. The magnetometer sensor will not sense people or animals walking beside it.

Passive Infrared ? The passive infrared sensor detects heat moving across its field of view. An average field of view has a range of 50 feet from the sensor and spreads out to 30 feet in a pie shape. Since automobile engines produce large amounts of heat, they are easy to detect with this type of sensor. An added advantage is that most passive infrared sensors will also detect people moving across their field of view. Passive infrared sensors draw very little current, so most manufacturers use this technology to make battery powered, wireless driveway sensors that do not require a cable run to the house. They transmit a coded radio signal to a Control Box in the house.

Control Box ? Either technology requires a control or receiver box in the house. This is where the signal from the sensor is converted into an output. The output may be a buzzer, chime sound, ding dong sound, or recorded voice. This sound is the audible indicator that a visitor is approaching. Options are available from different manufacturers to select the audible sound generated by the control box or eliminate it all together and use a relay output that can be connected to the home automation system.

Connecting the driveway sensors output to the home automation system is where the real convenience to the home owner is made available. Consider these features that can be enabled with a home automation controller or programmable controller connected to the control box through the control box? relay output:

When it is night time, turn on the outside lights for a programmed period of time when a vehicle drives up the driveway.
Make a voice announcement in the house that a visitor is approaching using a recorded voice annunciator.
When away from home and the security system is armed, make a warning voice announcement outside for the visitor to leave.
Welcome the visitor to a home or business.
Protect vehicles parked outside from vandals.
Activate video cameras when a visitor arrives.

A good understanding of the Pro?s and Con?s of both technologies is needed to use the right sensor in the proper application:



Passive Infrared


Normally below ground 6 to 8 inches

Mount to post or fence above ground


Sensor powered from Control Box AC plug-in or battery

Sensor battery powered, receiver AC plug-in

Sensing Range

15 feet, varies with sensor probe

50 feet from sensor, 30 feet across


Metal, steel moving

Heat moving, cars, people


Hidden from vandals

Subject to vandalism

Sensor distance from Control Box

10 to 2500 feet of cable run, 1000 feet Radio transmission

Up to 1000 feet, 2500 feet available, Radio transmission

Max. sensors to Control Box

2 sensors available

4 sensors available

Equipment prices for the Do-It-Yourselfer cover a broad range from as low as $25.00 to near $1000.00 according to features desired. The infrared type or wireless system will be less expensive because there will not be the added expense of the buried cable to the house.
Partial List of Driveway Alarm Manufacturers
Infrared Type

Miltronics Manufacturing, Inc., Keene, NH
Optex Wireless 1000, Optex America, Inc., Torrance, CA

Magnetometer Type

Cartell Driveway Sensors by Preferred Technologies Group ? Lancaster, PA
Mier Products, Inc., Kokomo, IN
Sure Action Incorporated, Westhampton Beach, NY
Winland Electronics, Inc., Mankato, MN