Driveway sensors are also known as driveway alarms, and "alarm" is exactly what they do. For many people, the driveway is the most direct route onto their property and in many cases the only route for a car or other vehicle.
Benefits of Driveway Sensors
By installing a driveway sensor, you will be able to receive notification that someone is using your driveway. There are many reasons why such information is valuable to a homeowner. Most important is the need to be alerted to unwanted trespassers. A single thief is bad enough, but thieves in a vehicle can rob you of much more than a single person or two can carry. You may also want to know when expected guests are arriving--before they actually knock on your front door. Owners of large rural properties often have long and winding driveways, so a glance out the front window isn't enough to alert you to impending visitors, expected or otherwise. Some high-end driveway sensors allow the alarm signal to be transmitted to a portable receiver. For ranchers repairing a fence or someone sunbathing in their back yard, having a remote receiver ensures that they'll never miss a visitor because they're unaware of their arrival.
Types of Sensor
There are many types of driveway sensors, reflecting the wide variety of different applications in which they are used. The simplest type of driveway sensor is a hardwired pressure-sensing device that closely resembles the bells used at old-time and rural gas stations. Because they are linked to their receiver via a wire, these devices are not practical when there is a long distance between the sensor and receiver. More advanced driveway sensors employ laser beams or magnetic field sensors, and most of these units are wireless.
Laser and Magnetic Sensors
Laser sensors use two fixed devices that activate an alarm when an object blocks the laser beam that "links" the two sender-receptor units. Better quality units can distinguish between vehicles and, say, a bird or wind-blown tumbleweed. Laser driveway sensors should always be installed by professionals as they need to be perfectly mounted and positioned in order to function as intended. Magnetic driveway sensors are electrically conductive metal sensing strips that are usually buried beneath the driveway. They can detect a vehicle's passing by the disruption in the magnetic field of the sensor. Only large metallic masses can activate the alarm. Once again, aim for the highest quality units: insufficiently sensitive units can be activated, often repeatedly, by nearby electrical storms.