Which icing are you chaps discussing?
Carb ice could be forecast by knowing the temp and DP, which is given in the ATIS (if there is ATIS) but you can also get electronic RH meters off the shelf; I have one for about £200 which I used to measure if keeping silica gel bags in the cockpit makes a decent difference (it does).
Carb ice can be avoided with a carb heater. But it is also aircraft type specific.
Structural ice comes from supercooled water droplets. These exist between 0C and about -15C (lower temp SLDs can be found in convective clouds), with the worst case around -5C. But you don't need a warning device. Just look out of the window onto the wing leading edge, and the elevator leading edge. At night you need a light (and deiced planes have such a light).