A movement detector for television signals measures the difference between maximum and minimum values of the movement components of a picture difference signal over a chosen interval. A television signal at an input (12) is delayed in a picture delay (2), and the delayed and undelayed signals subtracted in a subtractor (1) to form a picture difference signal. This is rectified in rectifier (3) and smoothed in a filter (4). A maximum detector (6) and a minimum detector (7) are coupled to the filter output and are re-set at prescribed intervals. A subtractor (8) determines the difference between the output of detectors (6) and (7) and this is compared with a reference value in a comparator (9), the output of which is sampled and stored in a store (10).