Dimethylamine, a secondary amine does not respond to carbylamine reaction. Carbylamine reaction can be used to identify primary amino group in a given organic compound.
When primary amines are treated with chloroform and alcoholic KOH, they give isocyanides (carbylamines) having very unpleasant smell which can be easily detected. RNH2+CHCl3+3KOH→RNC+3KCl+3H2O