Abstract: A device for monitoring the physical activity of persons comprises a movement detector 8 electrically coupled to drive time-delay circuits [C2, R2, TR6, R6,][C4, R4, TR4, R5][C5, R7, TR8, R8,] the outputs of which are connected to drive an alarm device 10 such that in the presence of the movements detected by detector 8 the alarm device 10 is held in its OFF condition and is switched to its ON condition in the absence of such movements after a pertaining time-delay. The time-delay circuits are respectively arranged to provide time-delays of 30 seconds, 6 seconds, 40 seconds, with the first and second time-delay circuits being connected in series and the third time-delay circuit connected in parallel with the first two so that if the first timer circuit activates the alarm the second timer circuit provides a delay prior to latching of the alarm during which the alarm can be manually cancelled while the third timer circuit provides for fail-safe operation.