A sensor that is sensitive to motion; a motion detector, especially as (part of) a security device that can trigger a burglar alarm, or as an aid to positioning or navigation.
Origin
1960s; earliest use found in Science.
Definition of motion sensor in US English:
motion sensor
noun
A sensor that is sensitive to motion; a motion detector, especially as (part of) a security device that can trigger a burglar alarm, or as an aid to positioning or navigation.