Definitions of scanner:

• noun:   a radio receiver that that moves automatically across some selected range of frequencies looking for for some signal or condition

  Example: "They used scanners to monitor police radio channels"

• noun:   a radar dish that rotates or oscillates in order to scan a broad area
• noun:   an electronic device that generates a digital representation of an image for data input to a computer
• noun:   someone who scans verse to determine the number and prosodic value of the syllables