A people counter is a device used to measure the number and direction of people traversing a certain passage or entrance per time unit. The resolution of the measurement is entirely dependent on the sophistication of the technology employed. The device is often used at the entrance of a building so that the total number of visitors can be recorded. Many different technologies are used in people counter devices, such as infrared beams, computer vision and thermal imaging. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Computer vision is the science and technology of machines that see wiki stranglesnakejpg|thumb|Thermographic image of a Snake held by a human]] Infrared Thermography, thermal imaging, or thermal video, is a type of
There are various reasons for counting people, the most common of which are:
Use of people counting systems in the retail environment is necessary to calculate the Conversion Rate, i. In Marketing, a conversion occurs when a prospective Customer takes the marketer's intended action e. the percentage of a store's visitors that makes purchases. This is the key performance indicator of a store's performance and is far superior to traditional methods, which only take into account sales data. Traffic counts and conversion rates together tell you how you got to your sales. i. e. if year-over-year sales are down: did fewer people visit my store, or did fewer people buy? Although traffic counting is widely accepted as essential for retailers, it is estimated that less than 25% of major retailers track traffic in their stores. 
Since staff requirements are often directly related to density of visitor traffic, accurate visitor counting is essential in the process of optimizing staff shifts.
Services such as cleaning and maintenance typically must be done when traffic is at its lowest or, occasionally, at a certain level. Planning of these activities necessitates accurate people counting.
For many locations it is essential to know how many people are inside the building at any given time, so that in the event of an evacuation they can all be accounted for. This can only be automated with the use of extremely accurate people counting systems.
Many public organizations use visitor counts as evidence when making applications for finance. In cases where tickets are not sold, such as in museums and libraries, counting is often required to be automated.
Many shopping center marketing professionals rely on visitor statistics to measure their marketing. Quite often shopping center owners measure marketing effectiveness with sales. A trend has been to include visitor statistics to scientifically measure marketing effectiveness. Marketing metrics such as CPM (Cost Per Thousand) and SSF (Shoppers per Square Foot) are becoming very useful key performance indicators.
Modern people counting systems use many different technologies, each with its own advantages and disadvantages. The main types are listed below.
The simplest form of counter is a single, horizontal infrared beam across an entrance which is typically linked to a small LCD display unit at the side of the doorway. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Such a beam counts a 'tick' when the beam is broken, therefore it is normal to divide the 'ticks' by two to get visitor numbers. Dual beam units are also available from some suppliers and can provide low cost directional flow 'in' and 'out' data. Accuracy depends highly on the width of the entrance monitored and the volume of traffic.
Vertical beams are somewhat more accurate than horizontal, with accuracies of over 90% possible if the beams are very carefully placed. Typically they do not give 'in and out' information, although some directional beams do exist.
Computer vision represents the state-of-the-art system for people counting. Computer vision is the science and technology of machines that see These typically use either a closed-circuit television camera or IP camera to feed a signal into a computer or embedded device. CCTV cameras can produce images or recordings for Surveillance purposes and can be either video cameras or digital stills cameras An embedded system is a special-purpose Computer system designed to perform one or a few dedicated functions often with Real-time computing constraints Some computer vision systems have integrated links to database systems and retail point of sale systems. Point of sale or point of service ( POS or PoS) can mean a retail shop, a checkout counter in a shop or the location where a transaction
Accuracy varies between systems and installations as background information needs to be digitally removed from the scene in order to recognize, track and count people. This means that CCTV based counters are vulnerable to light level changes and shadows, which can lead to inaccurate counting. If light levels are constant then high accuracy can be achieved, but counting at street level entrances, for example, can be inconsistent when sunlight shines into the view and then clouds move in front of the sun and the view then darkens. Sophisticated algorithms must be implemented to compensate for this behavior.
Thermal imaging systems use sensors which detect heat sources, rather than using cameras as in computer vision systems. wiki stranglesnakejpg|thumb|Thermographic image of a Snake held by a human]] Infrared Thermography, thermal imaging, or thermal video, is a type of These systems are typically implemented using embedded technology.
This system employs multiple IR transceivers to create a count zone at ankle height. The artificial intelligence counters function in a similar way to the human brain, in other words, each event is evaluated in terms of features to determine the correct outcome i. e. count per direction. As a person passes the count zone a pattern is generated. The onboard processor extracts the features of the pattern and based on what it has been taught makes a decision regarding the event by brute force calculation.