Traditional ground sensors employed a loop of cable in the ground. A vehicle part within the boundaries of the ground loop will be detected by induction. The ground loop is connected to a loop detector module in the gate or barrier control panel.

A new style of vehicle sensors are emerging for the purpose of activation. These new devices are known as single point exit sensors. They are dropped into a hole in the road surface and connect back to a detector module in the control  panel.

Some single point sensors have the detection circuit embedded in the sensor. These type can be used as a presence device as well as for activation.

There are several technologies for remotely identifying a device left in a vehicle, plus "number Plate Recognition" which identifies the vehicle.

Easy systems just require a card or dongle somewhere in the vehicle, alloing it to be transfered to rental cars or to friends. But keys can be stollen, and of course it is a gift to a theif stealing your car off your drive! 

This is the most convenient system and so is favoured by domestic users. A USB dongle is supplied for each vehicle, and active when plugged into a USB charger socket in the car.

The dongle is paired with every gate or barrier that it is authorised to enter. The receiver (shown in the photo) is wired into the gate or barrier control panel. It can be set to close the gate or garage door when the ignition is switched off

Some models have adjustable range. All are 20-80m.

We are all familiar with proximity card access. Range is limited by the power of the card to transmit its code. Active cards have a battery inside which allows long range systems to work up to 12 metres.

Like the WiFi reader, they are as convenient as mounting a card in a vehicle's wind screen. The antenna increases in size as the range extends, and systems are expensive. It is far from ideal for smart home entrances which is the growth area.

Secure tracker devices are fitted to public service and fleet vehicles. There is a significant installation cost to instal toeach vehicle, or to transfer between vehicles. 

Applications include access for emergency vehicles such as airfileds, and for restricted areas such as bus lanes, and one way access.

These devices have a unique code that is transmitted to a loop in the ground, so there is also a site installation cost. Their advantage is being able to target the area the vehicle is in.

In the past, photobeams have been used as activation devices, but do not discriminated between vehicles and pedestrians. Technology and techniques have advanced.

LiDAR sensors (as photo) use range finding ToF lasers to select a target. A sensor can be placed by the side of the road set to ignore pedestrians on a pavement. The beam is narrow and selective, so set high can filter out animals and children. 

For selective activation purposes, two beams can be wired to select objects greater than 4m long (a car) and detect the direction of travel. They are cheaper to instal ground sensors.

They also have safety applications, but these are beyond the scope of this  website.

AIR active Infrared sensors detect presence by reflection of IR emitted by the sensor. PIR passive infrared sensors only detect movement of IR emitting objects. These sensors are not very selective, but have been included because they are designed to focus down on the target. 

There is a wired version FAT10 and a wireless version FAR10, which is attractive on sites with poor infrastructure.

The ultimate vehicle recognition technology is NPR, because it identifies the vehicle, not the driver, or an ID device inside the vehicle.

NPR the gold standard 

NPR is accurate when it makes a positive ID, but some poor plates will come back with no positive ID. The security is underwritten by the state's intollerance of missing, damaged, or false plates. When NPR was first introduced in UK in 1981 when cameras had poor resolution and recognition software was slow. Accuracy is still not 100%.

Applications

Most NPRs are found on private car parks providing fast access to regular users. More recently, revenue car parks are using NPR in place of ticket dispensers. This also includes limited stay facilities such as transport hub drop off areas. There are 11,000 cameras on public roads in UK for traffic and speed enforcement.

State of art

It is not surprising that the phone in your pocket can upload an NPR app. The software is embedded in bullet cameras available at a price that is accessibly to domestic gate automation. Learning a new number plate however is still likely to be via a data from a laptop or tablet.

Position

Night view cameras are excellent, but no match for the glare of a car headlight on full beam. So cameras need to be positioned facing downwards towards the plate and at a distance of greater than 3m.