Radar-gun technology - just like the police and baseball scouts use - has arrived in toyland. The Hot Wheels Radar Gun ($20 to $30 retail) is designed to measure the velocity of Mattel's famous miniature race cars, but also will work on life-size bicycles, scooters, SUVs and thrown baseballs, if you aim it right. The gun isn't as precise as professional models but does employ genuine radio-wave radar. A switch will multiply the speed of 1/64-scale Hot Wheels cars by 64 - to display some lawbreaking m.p.h. numbers.