Definition of "Scanner" :

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

"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