The transmitter and receiver for the radalt is on the underside of the fuselage. So at 10 feet radalt the wheels are just above the runway. The main danger of this in practical terms is if you had cracked the reversers open in the flare, by raising the reverse levers a bit too soon, and then initiated a go around. This could happen on a low visibility approach if you found yourself close to the edge of the runway or with a runway incursion as you are about to touch down. The reversers should stow but if the system stays in the ground mode they will not and then you have a dangerous situation.
Yes air/ground safety sensor is american for squat switch (why use two words when four will do!).
