The hi-tech transparent device is about the size of a large multivitamin pill. It contains a rapidly rotating laser that shines a beam of near-infrared light on to the wall of the oesophagus, or gullet, the pipe that carries food to the stomach.
Sensors record the light reflections and produce detailed microscopic images that can reveal cell changes associated with Barrett's oesophagus, a pre-cancerous condition linked to heartburn and acid reflux.
A string-like tether allows the device to be pulled back up and transmits images to a monitor.
In tests on 13 unsedated volunteers, including six with Barrett's oesophagus, the capsule imaged the gullet in less than a minute, US scientists said in the Nature Medicine journal.
Current screening methods take well over an hour.