palgia, I'm aware of a low tech 'protuberance' that was used on the RAF model of the VC10. I don't know if it was fitted to the civil machines. It consisted of a black aerofoil shaped rod about 6 inches long, sticking out of the fuselage just below the Captain's window. In icing conditions it would ice up and the skipper could see the ice with his Mk 1 eyeball. It had a three position, centre off switch that when operated one way lit a lamp to check the probe at night and in the other position switched on a heater to clear ice off the probe - so you could see if it iced up again. The aircraft also had the rotary detector described above.