Parking sensors are proximity sensors for road vehicles designed to alert the driver of obstacles while parking. These systems use either electromagnetic or ultrasonic sensors.
These systems feature ultrasonic proximity detectors to measure the distances to nearby objects via sensors located in the front and/or rear bumper fascias or visually minimized within adjacent grills or recesses.
The sensors emit acoustic pulses, with a control unit measuring the return interval of each reflected signal and calculating object distances. The system in turns warns the driver with acoustic tones, the frequency indicating object distance, with faster tones indicating closer proximity and a continuous tone indicating a minimal pre-defined distance. Systems may also include visual aids, such as LED or LCD readouts to indicate object distance. A vehicle may include a vehicle pictogram on the car's infotainment screen, with a representation of the nearby objects as coloured blocks.
Rear sensors may be activated when reverse gear is selected and deactivated as soon as any other gear is selected. Front sensors may be activated manually and deactivated automatically when the vehicle reaches a pre-determined speed -- to avoid subsequent nuisance warnings.
As an ultrasonic systems relies on the reflection of sound waves, the system may not detect flat objects or object insufficiently large to reflect sound -- e.g., a narrow pole or a longitudinal object pointed directly at the vehicle or near an object. Objects with flat surfaces angled from the vertical may deflect return sound waves away from the sensors, hindering detection. Also soft object with strong sound absorption may have weaker detection, e.g. wool or moss.
The Parking Sensor, originally called as ReverseAid, was a spin-off from the Sonic Pathfinder, an Electronic Guidance Device for the Blind. Both devices were invented in the late 1970s by Tony Heyes while working at the Blind Mobility Research Unit at Nottingham University in the UK. After patenting the device in 1983 Heyes offered it to Jaguar Cars in Coventry. After test driving the prototype on Heyes's car they very politely told him that, "You like it because you are a one-eyed driver who cannot judge distances. Real people would not want a thing like this."
Heyes teamed up with a local manufacturer and some 150 units were made and fitted to petrol tankers, trucks and delivery vehicles. Very few were fitted to private cars since few people wanted to drill holes in their cars.
The electromagnetic parking sensor (EPS) was re-invented and patented in 1992 by Mauro Del Signore. Electromagnetic sensors rely on the vehicle moving slowly and smoothly towards the object to be avoided. Once detected, the obstacle, if the vehicle momentarily stops on its approach, the sensor continues to give signal of presence of the obstacle. If the vehicle then resumes its manoeuvre the alarm signal becomes more and more impressive as the obstacle approaches. Electromagnetic parking sensors are often sold as not requiring any holes to be drilled offering a unique design that discreetly mounts on the inner side of the bumper preserving the 'new factory look' of your vehicle. Now they also come equipped with a camera to go with the sensor. By 2018 the US is requiring back up camera with sensors on all cars.
Blind spot monitors are an option that may include more than monitoring the sides of the vehicle. It can include "Cross Traffic Alert," "which alerts drivers backing out of a parking space when traffic is approaching from the sides."
Already in the 1970s German inventor Rainer Buchmann developed parking sensors. December 13, 1984 Massimo Ciccarello and Ruggero Lenci (see List of Italian inventors) entered in Italy the patent request for ultrasonics Parking sensors, and November 16, 1988 the Ministry of Industry granted them the Patent for industrial invention n. 1196650.