There are four different types of bar-code readers, each using a different technology to read a bar code. As of 2014, the types are charge-coupled devices, camera-based devices, pen devices and laser scanners. These devices read encoded information within a bar code's visual pattern and convert it into readable data.
Charged-couple-device readers use arrays of light sensors. These arrays consist of hundreds of small light sensors aligned in a row within the head of the reader. Charged-couple-device readers detect ambient light emitted from a bar code and generate a voltage pattern identical to the pattern shown within the bar code. Camera-based readers are the most recently invented readers, as of 2014, and they use a video camera to capture the bar code's image. Camera-based readers use the same technology as charged-couple-device readers, the difference being that camera-based readers use hundreds of rows of sensors to generate an image instead of using a single sensor.
Pen types read bar codes by measuring the intensity of the light reflected by the bar code using a light source and a photo diode. A pen-type reader is used by dragging the tip of the pen across the bar code in a steady motion. The photo diode in a pen sensor then emits a voltage waveform that is an exact replica of the bars and spaces patterned within the bar code. The waveform is then decoded by the scanner. Laser scanners work the same as pen readers but use a laser beam as the light source.