Abstract: An add-on track system for an all-terrain vehicle is disclosed. ATV tires are very soft and flexible, and apt to climb out of a track if the track is not properly located. The invention has a track segment with arms protruding up from the slope-plate of the segment, and the arms converge inwards. The upper ends of the arms locate the segment against the tire side walls, but at a level on the sidewalls where the tire profile is free of the bulging under load which is so marked in ATV tires. The segments have holes through the sole-plate, through which the overhanging parts of the converging arms can be moulded, without movable cores. Retractable cleats occupy these holes, and are forced out when the tire bulges under load.

Abstract: An ultrasonic intrusion alarm is described. In the specific embodiment described with reference to the drawings, the alarm includes a transmitter and a receiver both mounted in a cylindrical housing. The housing is turnably held in contact with a base by a grill cloth. In use the housing is turned to direct the transmitter. The grill cloth prevents the area protected by the alarm being visually determined from externally of the alarm.