A card reader is a data input device that reads data from a card-shaped storage medium. The first were punched card readers, which read the paper or cardboard punched cards that were used during the first several decades of the computer industry to store information and programs for computer systems. Modern card readers are electronic devices that can read plastic cards embedded with either a barcode, magnetic strip, computer chip or another storage medium.
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A reader radiates a 1" to 20" electrical field around itself. Cards use a simple LC circuit. When a card is presented to the reader, the reader's electrical field excites a coil in the card. The coil charges a capacitor and in turn powers an integrated circuit. The integrated circuit outputs the card number to the coil, which transmits it to the reader.
Wiegand card technology is a patented technology using embedded ferromagnetic wires strategically positioned to create a unique pattern that generates the identification number. Like magnetic stripe or barcode technology, this card must be swiped through a reader to be read. Unlike the other technologies, the identification media is embedded in the card and not susceptible to wear. This technology once gained popularity because it is difficult to duplicate, creating a high perception of security. This technology is being replaced by proximity cards, however, because of the limited source of supply, the relatively better tamper resistance of proximity readers, and the convenience of the touch-less functionality in proximity readers. 

Sometimes memories can fade in time, but then we can experience something which brings decade’s old memories flooding back. It could be finding an old photograph, the feel of something in our fingers, the sound of seagulls squawking overhead or the smell from a bakery wafting in the breeze as we are walking along the street. Then, just for a moment, it is as though we are right back in that once-forgotten moment, experiencing the joy and happiness as though reliving it.

An important feature for memory card readers is the speed with which they can transmit data. Readers with USB 3.0 compatibility will be faster than USB 2.0 technology (as long as your computer has a USB 3.0 port). As mentioned earlier, there are various types of memory cards, so having a reader than can communicate with more than one interface will be beneficial, especially if you find yourself using multiple memory cards.
A common proximity format is 26-bit Wiegand. This format uses a facility code, sometimes also called a site code. The facility code is a unique number common to all of the cards in a particular set. The idea is that an organization will have their own facility code and a set of numbered cards incrementing from 1. Another organization has a different facility code and their card set also increments from 1. Thus different organizations can have card sets with the same card numbers but since the facility codes differ, the cards only work at one organization. This idea worked early in the technology, but as there is no governing body controlling card numbers, different manufacturers can supply cards with identical facility codes and identical card numbers to different organizations. Thus there may be duplicate cards that allow access to multiple facilities in one area. To counteract this problem some manufacturers have created formats beyond 26-bit Wiegand that they control and issue to organizations.
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A contactless smart card uses the same radio-based technology as the proximity card, with the exception of the frequency band used: it uses a higher frequency (13.56 MHz instead of 125 kHz), which allows the transfer of more data, and communication with several cards at the same time. A contactless card does not have to touch the reader or even be taken out of a wallet or purse. Most access control systems only read serial numbers of contactless smart cards and do not utilize the available memory. Card memory may be used for storing biometric data (i.e. fingerprint template) of a user. In such case a biometric reader first reads the template on the card and then compares it to the finger (hand, eye, etc.) presented by the user. In this way biometric data of users does not have to be distributed and stored in the memory of controllers or readers, which simplifies the system and reduces memory requirements.
Sometimes memories can fade in time, but then we can experience something which brings decade’s old memories flooding back. It could be finding an old photograph, the feel of something in our fingers, the sound of seagulls squawking overhead or the smell from a bakery wafting in the breeze as we are walking along the street. Then, just for a moment, it is as though we are right back in that once-forgotten moment, experiencing the joy and happiness as though reliving it.
A barcode is a series of alternating dark and light stripes that are read by an optical scanner. The organization and width of the lines is determined by the bar code protocol selected. There are many different protocols, such as the prevalent Code 39.[3] Sometimes the digits represented by the dark and light bars are also printed to allow people to read the number without an optical reader.

In the 1-to-1 mode a user must first either present an ID card or enter a PIN. The reader then looks up the template of the corresponding user in the database and compares it with the live scan. The 1-to-1 method is considered more secure and is generally faster as the reader needs to perform only one comparison. Most 1-to-1 biometric readers are "dual-technology" readers: they either have a built-in proximity, smart card or keypad reader, or they have an input for connecting an external card reader.