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.
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.
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The advantage of using barcode technology is that it is cheap and easy to generate the credential and it can easily be applied to cards or other items. However the same affordability and simplicity makes the technology susceptible to fraud, because fake barcodes can also be created cheaply and easily, for example by photocopying real ones. One attempt to reduce fraud is to print the barcode using carbon-based ink, and then cover the bar code with a dark red overlay. The barcode can then be read with an optical reader tuned to the infrared spectrum, but can not easily be copied by a copy machine. This does not address the ease with which barcode numbers can be generated from a computer using almost any printer.
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.