History
The bio-sensor was a Skrull device, about the size of an early 21st century tablet. Which could identify the presence of lifeforms. When the Avengers sneaked into the Power Asteroid disguised as human-looking Skrulls from the Big Casino, one of the Skrulls in the dock had a bio-sensor. It gave him readings stating that there were five additional lifeforms on the dock, not just the four newcomers that were visually evident.[1]